Program - Symposium CC: Optically Active Nanostructures

2012 MRS Fall Meeting

2012 MRS Fall Meeting & Exhibit

November 25-30, 2012Boston, Massachusetts
Download Session Locator (.pdf)2012-11-26  

Symposium CC

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Symposium Organizers

  • Matthew Doty, University of Delaware
  • Srikanth Singamaneni, Washington University
  • Andrey L. Rogach, City University of Hong Kong
  • Mark Brongersma, Stanford University
  • Vladimir V. Tsukruk, Georgia Institute of Technology

    CC1: Colloidal Nanomaterials

    • Chair: Ulrike Woggon
    • Monday AM, November 26, 2012
    • Hynes, Level 2, Room 208
     

    8:30 AM - *CC1.01

    Surface Plasmon Enhanced Non-radiative Energy Transfer in Planar Quantum Dot Structures

    Xia  Zhang1, Manuela  Lunz1, Valerie  A.  Gerard2, Yurii  K.  Gun'ko2, Vladimir  Lesnyak3, Nikolai  Gaponik3, Andrei  S.  Susha4, Andrey  L.  Rogach4, Louise  Bradley1.

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    Energy transport on the nanoscale via non-radiative energy transfer (NRET) is extensively studied for applications in areas such as light-harvesting, colour conversion, colour tuning and sensors. Quantum dots (QDs) are of particular interest for many applications due to their size tunable emission, broad absorption and good photostability. However, in QD solid structures the non-radiative energy transfer distance is typically less than 10 nm, placing a severe restriction on potential device designs and architectures. It has been shown that non-radiative energy transfer can be enhanced through interaction of the energy donor and energy acceptor with localized surface plasmons. CdTe QD sandwich structures, incorporating a monolayer of gold spheres, have been used to study surface plasmon modified NRET. The concentrations and separations of the constituent QD and gold nanoparticle monolayers can be independently controlled. The monolayer of 5.5 nm diameter gold nanoparticles has a localized surface plasmon peak overlapping the donor emission and acceptor absorption of the energy transfer pair. Strong enhancement of the rate and distance over which NRET occurs is observed. A surface plasmon enhanced NRET efficiency of 21% was measured in a sandwich structure with a donor to acceptor separation of ~24 nm. In the absence of the gold nanoparticle layer a NRET efficiency of 0.14% is expected over this distance. Further investigation shows a strong dependence of the surface plasmon NRET mechanism on the gold nanoparticle concentration and different regimes are identified. At the lowest gold nanoparticle concentrations investigated an overall enhancement of the acceptor emission can be observed. At higher gold nanoparticle concentrations the energy transfer rates are further increased, however, this reduces acceptor QD emission due to quenching effects.

    9:00 AM - CC1.02

    Size Quantization of Plasmons in Metallic Nanoparticle Dimers and Quantum Dot/MNP Systems

    Emily  Townsend1, G.  W.  Bryant1.

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    The transfer of quantum information between various systems is desirable for most applications of quantum resources. One realization of quantum information transfer uses a composite system of metallic nanoparticles (MNP) and semiconductor quantum dots (QD), with plasmons in MNPs moving qubits from QD to QD. An accurate description of this process requires an understanding of the coupling and hybridization between states of the QD and the MNP plasmons. Ultimately a quantum description of an entire composite system, potentially including multiple MNPs, and multiple QDs, is needed. To this end, we apply real-time, real-space Time-Dependent Density Functional Theory to systems of MNPs and QDs. Here we examine MNP dimers (Au jellium nanospheres) and systems of one MNP and one QD. The quantum dots are modeled as spherically symmetric finite square wells with two bound states, one filled and one empty. In previous work, we showed that the optical response of single small MNPs consists of “quantum core plasmons”, charge density oscillations primarily localized near the center of the MNP, and “classical surface plamons”, charge density oscillations throughout the particle [1]. We showed that both of these are collective oscillations, and that as the size of the MNP increases, there is a transition to classical behavior. Widely separated MNP dimers behave similarly to isolated MNPs. However as they are brought more closely together, the resonances split and shift as a result of hybridzation. We examine the spatial character of the resonances, comparing them to the quantum core plasmons and classical surface plasmons seen in the single MNP to determine how size quantization modifies the plasmon hybridization. Results for the QD/MNP composite system will be discussed to show how hybridization with a discrete excitation differs from plasmon hybridization in this regime. [1] E.Townsend, G.W. Bryant, Nano Lett. 12(1), 429 (2012).

    9:15 AM - CC1.03

    The Plasmoelectric Effect in Electrically Contacted Ag and Au Colloidal Nanoparticles

    Matthew  Sheldon1, Ana  M.  Brown1, Harry  A.  Atwater1.

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    We have recently proposed the plasmoelectric effect as a new physical mechanism for conversion of optical power into DC electrical power using an all-metal circuit [1,2]. When a plasmonic nanostructure is free to exchange charge density through an electrical connection, heat from optical absorption near the plasmon resonance frequency can be converted into an electrochemical potential, i.e. a plasmoelectric potential, that drives current through a circuit load. Unlike the more familiar thermoelectric or photovoltaic effects, the magnitude and sign of the plasmoelectric potential depends on the frequency difference between the plasmon resonance and the incident radiation. Radiation at higher frequencies induces an increase of electron density in the nanostructure that blue-shifts the plasmon resonance. This response is thermodynamically favored due to the increased entropic heat that accompanies the increased absorption. Similarly, radiation at lower frequencies decreases electron density in the nanostructure to induce a red-shift of the absorption maximum. We experimentally test these unique predictions by characterizing the electrical response of colloids of monodisperse Au or Ag nanoparticles spin-cast on ITO films. Kelvin probe force microscopy (KPFM) provides nanoscale resolution of the surface potential of the device structure while varying the frequency of incident radiation near the plasmon resonance. Further, the ensemble optoelectronic response of samples can be determined by photoelectrochemical measurements in which the plasmoelectric structure is immersed in an electrolyte and the sign and magnitude of the photovoltage is measured with respect to a counter electrode while varying incident wavelength. We observe clear evidence for the size-dependent and frequency-dependent trends in electrochemical potential consistent with our theoretical framework for the plasmoelectric effect. Our results provide deeper insight into the efficiency of optical power conversion via the plasmoelectric effect, practical considerations, and further applications of this new class of optoelectronic phenomenon. [1] “The plasmoelectric effect: optically induced electrochemical potentials in resonant metallic structures” Matthew T. Sheldon, Harry A. Atwater, 2012, in submission, arXiv:1202.0301 [2] “The plasmoelectric effect: conversion of optical power into DC electrical power by plasmonic nanostructures in all-metal circuits”, Matthew T. Sheldon, Harry A. Atwater, oral presentation, Symposium KK, MRS Spring Meeting, 2012

    9:30 AM - CC1.04

    CdTe/Cu2-xTe Nanorod Heterostructures for Investigating Exciton-plasmon Interactions

    Ilka  Kriegel1, Jessica  Rodriguez-Fernandez1, Andreas  Wisnet2, Enrico  Da Como3, Alexander  O.  Govorov4, Jochen  Feldmann1.

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    Heterostructures consisting of different materials within one nanoparticle are interesting for investigating the coupling of electronic excitations at the nanoscale. The model nanosystems investigated so far mainly consisted of two semiconductors, as they offer the possibility of designing their relative band alignment across the interface, resulting in type I and type II heterostructures. However, there is an increasing interest in focusing on the electronic coupling between semiconductor and metal nanoparticles and their fundamental excitations, namely exciton-plasmon interactions.[1] Such studies have up to now been limited to hybrid structures, where the metal is attached to the semiconductor by chemical means. Recently, copper chalcogenide (Cu2-xTe, E=S, Se, Te) nanocrystals (NCs) have been shown to offer the unique property of holding excitons and highly tunable plasmon resonances in one material.[2] As such, they are envisaged as an appealing material for the investigation of exciton-plasmon interactions at different levels of coupling. However, an excess of free charge carriers, an inherent property of this material class, adds additional pathways for the exciton to recombine, for example via Auger recombination. In this contribution we report on the synthesis of heterostructured nanorods consisting of CdTe and Cu2-xTe via partial ion-exchange. In this type of heterostructure the exciton of CdTe interacts with the plasmon resonance of Cu2-xTe as they overlap in energy. A unique property of this material is the possibility to control (enhance or suppress) the plasmon resonance in Cu2-xTe, as demonstrated previously.[2] This creates a material system in which the exciton within the same nanostructure can be investigated with and without exciton-plasmon interactions. This allows to directly address the influence of the plasmon resonance on the excitonic properties. We demonstrate that the suppression of the plasmon resonance in Cu2-xTe leads to a recovery and red-shift of the CdTe fluorescence arising from the radiative recombination of the exciton. We further show that the exciton dynamics is altered in the presence of the plasmon resonance, and support our results by theoretical calculations. In particular, we calculate the effect of exciton-plasmon Coulomb interaction on the absorption spectra of CdTe/Cu2-xTe nanocrystals using the microscopic model. [1] Lee, J.; Hernández, P.; Lee, J.; Govorov, A. O.; Kotov, N. A., Exciton-plasmon interactions in molecular spring assemblies of nanowires and wavelength-based protein detection. Nat Mater 2007, 6 (4), 291-295. [2] Kriegel, I.; Jiang, C.; Rodríguez-Fernández, J.; Schaller, R. D.; Talapin, D. V.; da Como, E.; Feldmann, J., Tuning the Excitonic and Plasmonic Properties of Copper Chalcogenide Nanocrystals. Journal of the American Chemical Society 2012, 134 (3), 1583-1590.

    9:45 AM -

    Break

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    10:15 AM - *CC1.05

    Optically-active Hybrid Nanostructures: Exciton-plasmon Interaction, Fano Effect, and Plasmonic Chirality

    Alexander  O  Govorov1.

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    Coulomb and electromagnetic interactions between excitons and plasmons in hybrid nanostructures lead to several interesting effects: Energy transfer between nanoparticles, plasmon enhancement, exciton energy shifts, Fano interference, and new mechanisms of optical chirality [1-6]. An interaction between a discrete state of exciton and a continuum of plasmonic states gives rise to interference effects (Fano-like asymmetric resonances and anti-resonances) [2,4]. These interference effects can strongly enhance a visibility of relatively weak exciton signals and can be used for spectroscopy of single nanoparticles and molecules. If a system includes chiral elements (chiral molecules or nanocrystals), the exciton-plasmon interaction is able to alter and enhance the circular dichroism (CD) of chiral components [5-8]. In particular, the exciton-plasmon interaction may create new chiral plasmonic lines in CD spectra of a biomolecule-nanocrystal complex [5,7]. Strong CD signals may also appear in purely plasmonic systems with a chiral geometry and a strong particle-particle interaction [6,8]. Recent experiments on the protein-nanocrystal and multi-nanocrystal complexes showed the appearance of strong plasmonic signals in CD spectra [7,8]. Potential applications of dynamic hybrid nanostructures include sensors and new optical and plasmonic materials. [1] A. O. Govorov, G. W. Bryant, W. Zhang, T. Skeini, J. Lee, N. A. Kotov, J. M. Slocik, and R. R. Naik, Nano Letters 6, 984 (2006). [2] W. Zhang, A. O. Govorov, G. W. Bryant, Phys. Rev. Lett. 97, 146804 (2006). [3] J. Lee, P. Hernandez, J. Lee, A.O. Govorov, and N. A. Kotov, Nature Materials 6, (2007). [4] M. Kroner, A. O. Govorov, S. Remi, B. Biedermann, S. Seidl, A. Badolato, P. M. Petroff, W. Zhang, R. Barbour, B. D. Gerardot, R. J. Warburton, and K. Karrai, Nature 451, 311 (2008). [5] A.O. Govorov, Z. Fan, P. Hernandez, J.M. Slocik, R.R. Naik, Nano Letters 10, 1374 (2010). [6] Z. Fan, A.O. Govorov, Nano Letters 10, 2580 (2010). [7] J.M. Slocik, A.O. Govorov, and R.R. Naik, Nano Letters 11, 701 (2011). [8] A. Kuzyk, R. Schreiber, Z. Fan, G. Pardatscher, E.-M. Roller, A. Högele, F.C. Simmel, A. O. Govorov, T. Liedl, Nature, 483, 311 (2012).

    10:45 AM - CC1.06

    CdHgTe Alloy Colloidal Quantum Dots: Tuning Optical Properties from the Visible to near-infrared by Ion Exchange

    Shuchi  Gupta1, Olga  Zhovtiuk1, Aleksandar  Vaneski1, Yan-Cheng  Lin2, Wu-Ching  Chou2, Stephen  Vincet  Kershaw1, Andrey L.  Rogach1.

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    The energy gap between valence and conduction levels in colloidal semiconductor quantum dots can be tuned via the nanoparticle diameter when this is comparable to or less than the Bohr radius. In materials such as cadmium mercury telluride which readily forms a single phase ternary alloy this quantum confinement tuning can also be augmented by compositional tuning, which brings a further degree of freedom in the bandgap engineering. Here we show how compositional control of 2.3nm diameter CdxHg(1-x)Te nanocrystals by exchange of Cd2+ and Hg2+ ions can be used to change their optical properties across a technologically useful range, from 500nm to almost 1200nm. We provide data on composition-dependent changes in the optical properties: bandgap; extinction coefficient; emission energy and spectral shape; Stokes shift; quantum efficiency; and radiative lifetimes as the exchange process occurs. These data are highly relevant for those seeking to optimise the materials and device designs. Our data allow for important insights into the cation exchange process in ternary nanocrystal alloys, which are consistent with a fast initial uptake of Hg2+ at the surface of the CdTe quantum dots, followed by a gradual interdiffusion of the two cations.

    11:00 AM - CC1.07

    Nano Colloids and Non-centrosymmetric Nanostructured Materials

    John  Gibbs1, Marcel  Pfeifer1 2, Andrew  Mark1, Tung Chun  Lee1, Peer  Fischer1.

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    We report the fabrication of structured, nanoparticles with total sizes < 100 nm using the thin-film physical vapor deposition technique known as glancing angle deposition, or GLAD. This process has previously been shown to allow for morphologies with features on the order of hundreds of nanometers up to a few microns with various geometries, but to the best of our knowledge, it has not been used as a step on the way to monodispersed suspensions of colloidal nanoparticles. Here we show that with the ease of fabrication combined with a large set of possible evaporation materials and nanostructure morphology control, GLAD can compete with and out-perform some of the best nanoparticle fabrication techniques in the synthesis of asymmetric and non-centrosymmetric nanoparticles with complex morphologies or compositions. We will also report on the well-known disadvantages of the technique which can be especially pronounced when growing nanoscale-featured particles. Examples include competitive growth of columns, column merging, and effects of adatom mobility; the latter directly counteracts the shadowing effect that we seek to exploit in order to fabricate nanoparticles with small feature sizes. We demonstrate ways to minimize these effects. To illustrate the effectiveness of the technique, we will outline a specific example of wafer-scale fabrication of helical oxide nanoparticles that in solution exhibit polarization-sensitive light scattering depending upon the enantiomorphic sense of the helix. The nanoparticles are fabricated on a substrate with GLAD, removed via sonication, and suspended with the help of a surfactant agent into a colloidal solution. We believe these are the smallest complex chiral colloids that have been grown to date. The fidelity of the grown structure to the design is verified by SEM and TEM analysis.

    11:15 AM - CC1.08

    Precise Location and Concentration of Dopant Insertion inside Colloidal Quantum Dots: Synthesis Strategy and Optical Properties

    Nathan  Grumbach1 2, Anna  Brusilovski1, Georgy  Maikov1, Evgeny  Tilchin1, Efrat  Lifshitz2.

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    The promise of colloidal quantum dots (CQDs) as a technological material, including light emitting diodes, gain devices, photovoltaic cells, spintronics, quantum information, sensors and biological platforms, demands high quality quantum dots. Ultimately, it may depend on tailoring their behavior through doping. Doping nanocrystals, and especially magnetic doping, leads to phenomena not found in the bulk as a result of confinement of carriers in a small volume. The strong sp-d exchange interactions between the charge carriers and the magnetic ion may result in a giant Zeeman splitting of the valence and conduction band states , a large Faraday rotation, or the formation of Magnetic Polarons (MPs), depending on the host nanocrystal . Exploration of all of these issues depends on having reliable methods to incorporate impurities. The most used strategy for doping is to include a precursor containing the impurity in the high temperature colloidal synthesis, which yields particles of high crystal quality . Nevertheless, it is often difficult to bring dopant into the bulk interior of nanoparticles by these methods, and the doping level is very low (typically an order of magnitude less than hoped). A colloidal synthesis strategy for doping nanocrystal is presented here, adapted for the synthesis of Mn-doped CdTe/CdSe core/shell CQDs. This strategy is based on a construction layer by layer of CQDs, allowing a more precise control of dopant location: inside the core, the shell, at the interface or on the surface of the NCs, concentration and properties, and can also be adapted to all variety of doping configurations, host material, size, shape, impurity location or amount. We gave evidence of successful doping, and shown an example in which optical properties of Mn-doped nanocrystals depends on extremely precise Mn position inside the nanoparticles. This includes large blue-shift in photluminescence spectra, differences between emission of polarized and non polarized photons or existence of two at least mechanisms for exciton recombination. Single-dot measurements, with or without polarization dependence offered us the opportunity to explore with a high resolution the giant magnetization and sp-d coupling in Mn-doped CQDs.

    11:30 AM - CC1.09

    Improved Precursor Chemistry for the Synthesis of III-V Colloidal Quantum Dots

    Daniel  Harris1, Moungi  Bawendi2.

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    Indium phosphide (InP) quantum dots (QDs) are of interest for applications that require cadmium-free, visible-emitting quantum dots, while indium arsenide (InAs) QDs are of interest for applications involving near infrared emission. However, InP and InAs QDs are challenging to synthesize with the tight size distributions readily achieved for cadmium selenide and lead selenide QDs. Rapid precursor conversion rates for the group-V precursors used in InP and InAs QD synthesis are believed to prevent the formation of a highly monodisperse QD ensemble. We have attempted to address this problem by seeking out less reactive precursor chemistries for these materials in hopes of improving QD size distributions. Tris(trimethylsilyl)arsine and tris(trimethylsilyl)phosphine have historically been used in InP and InAs QD synthesis, however these molecules are pyrophoric, and challenging to synthesize and manipulate. By eliminating the silicon-group V bond, we have identified new phosphorous and arsenic precursors that are less reactive than existing precursor chemistries and produce QDs with superior size distributions. To compare the effect of precursor chemistry on QD ensemble size distribution, we have synthesized QDs under identical conditions and varied the precursor. Ensemble size distribution was inferred from the shape of the absorption spectra. We characterized the reactivity of the precursors using UV-Vis absorption spectroscopy to quantitatively observe the rate of formation of QDs. The molecular precursor conversion was monitored using NMR spectroscopy. Our results show that the development of less reactive group-V precursors is a way forward toward the improvement of III-V QD synthesis.

    11:45 AM - CC1.10

    Controlling the Catalyst in Photocatalytic Hydrogen Generation with Colloidal Semiconductor Nanocrystals

    Frank  Jaeckel1, Maximilian  Berr1, Florian  Schweinberger2, Aleksandar  Vaneski3, Andrei  Susha3, Andrey  Rogach3, Martin  Tschurl2, Ulrich  Heiz2, Jochen  Feldmann1.

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    Metal-decorated colloidal nanocrystals are receiving great interest for photocatalytic hydrogen generation. [1-3] Here we report how controlling the catalyst cluster influences the hydrogen generation efficiency. First, we show that catalysts based on different metals show drastically different hydrogen generation quantum efficiencies. Second, we control the catalyst particle size and coverage by size selected cluster deposition under UHV conditions and show that the hydrogen generation efficiency depends on both these parameters. Finally, we demonstrate that the efficiency and stability of the nanocrystals can be tuned via the redox potential of the hole scavenger [4]. [1] M. Berr, A. Vaneski, A. S. Susha, J. Rodríguez-Fernández, M. Döblinger, F. Jäckel, A. L. Rogach, J Feldmann Appl. Phys. Lett. 97, 093108 (2010). [2] A. Vaneski, A.S. Susha, J. Rodriguez-Fernandez, M. Berr, F. Jäckel, J. Feldmann, A.L. Rogach, Adv. Funct. Mater. 21(9), 1547-1556 (2011). [3] M.J. Berr, A. Vaneski, C. Mauser, S. Fischbach, A.S. Susha, A.L. Rogach, F. Jäckel, J. Feldmann, Small 8(2), 291-297 (2012) . [4] M.J. Berr, P. Wagner, S. Fischbach, A. Vaneski, J. Schneider, A.S. Susha, A.L. Rogach, F. Jäckel, J. Feldmann Appl. Phys. Lett. 100, 223903 (2012).

    CC2: Photonic and Optical Devices

    • Chair: Alexander Govorov
    • Monday PM, November 26, 2012
    • Hynes, Level 2, Room 208
     

    1:30 PM - *CC2.01

    Quantum Dot-photonic Crystal Based Optoelectronic Devices Operating at the Quantum Limit

    Jelena  Vuckovic1, Michal  Bajcsy1.

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    Quantum dots (QDs) in photonic crystal nanocavities provide a scalable, on-chip, semiconductor platform for the study of cavity QED, but also enable very large dipole-field interaction strengths, as a result of the field localization inside of sub-cubic wavelength volumes (vacuum Rabi frequency is in the range of 10's of GHz). Moreover, this platform can be employed to build devices for quantum information processing, such as ultrafast quantum gates, nonclassical light sources, and spin-photon interfaces. We have demonstrated controlled amplitude and phase modulation between two optical beams at the single photon level (power less than a photon per cavity photon lifetime) interacting via a strongly coupled quantum dot - photonic crystal cavity system, with the switching speed of 25GHz. We have also studied the effects of the photon blockade and photon induced tunneling which result from the anharmonicity of the ladder of dressed states in a strongly coupled QD-nanocavity system. These effects lead to dramatic changes in the transmitted photon statistics, which can be varied from sub-Poissonian to super-Poissonian, and can be employed to generate nonclassical states of light (such as Fock or NOON states) with high efficiency. Beside quantum information systems, many classical information processing devices greatly benefit from the enhanced light matter interaction in such structures; examples include all-optical switches, electro-optic modulators controlled with sub-fJ energy and operating at GHz speed, and lasers with threshold currents of 100nA.

    2:00 PM - CC2.02

    Design and Fabrication of High Quality Factor InGaN/GaN Optical Cavities

    Alexander  Woolf1, Igor  Aharonovich1, Kasey  J.  Russell1, Nan  Niu1, Christine  Zgrabik1, Tongtong  Zhu2, Haitham  A.R.  El-Ella2, Menno  J.  Kappers2, Rachel  A.  Oliver2, Evelyn  L.  Hu1.

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    Recent advances in the growth and fabrication of III-V nitrides have allowed for the realization of optically efficient light emitters in the blue spectral range. However, in spite of such achievements the chemical inertness, high defect densities, and internal fields in these materials have hindered progress towards the next generation of devices such as low threshold lasers, single photon sources, and room temperature Bose-Einstein condensates. Here we report on the optimization of material design and fabrication techniques of gallium nitride microdisk cavities which has allowed us to realize structures with record high quality factors (~10,000) and low threshold, room temperature lasing. We will present data on the influence of the disk membrane thickness as well the number of layers of quantum dots (1 vs 3) on the performance of the devices. We will discuss optimization of lithography, masking and etching techniques to provide smooth sidewalls and effective undercut isolation through photoelectrochemical etching. Such considerations are critical in achieving enhanced future performance of optical devices in this material system.

    2:15 PM - CC2.03

    Optically Active InGaAs/GaP Quantum Dots for Integrated Lasers

    Holger  Eisele1, Christopher  Prohl1, Dominik  Roy1, Andrea  Lenz1, Josephine  Schuppang1, Gernot  Stracke1, Andre  Strittmatter1, Udo  W.  Pohl1, Mario  Daehne1, Dieter  Bimberg1.

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    Electrical chip-to-chip connections have not been improved a lot in speed during recent years.Hence, the demand for optical connections gets more and more important. Therefore, the integration of optically active semiconductor structures on silicon is necessary. During the last years, the direct integration of GaP on Si has been much improved by solving the anti-phase domain problem between at the interface between them. Now, an optically active layer within GaP is necessary to drive lasers integrated on Si devices. In this contribution we studied the structural properties of InGaAs quantum dots within GaP, which is potentially an optically active system for the direct integration on Si devices. From an analysis of the spatial structure at the atomic scale by cross-sectional scanning tunneling microscopy we can conclude on the one hand how the growth works in detail, as well as on the other hand we can provide data for the simulation of the optical parameters. The InGaAs quantum dot structures was grown using metal-organic chemical vapor deposition on GaP(001) substrates. For planarization first a GaP buffer was grown, on which the active layer was deposited. Afterwards, they were covered again by GaP, as necessary for a device structure. The InGaAs/GaP quantum dot are found to have a truncated pyramidal shape, with a distinct (001) bottom and top interface, very similar to InAs/GaAs quantum dots. The indium concentration shows a reversed cone stoichiometric profile, as typically also found upon co-deposition of In and Ga during quantum dot growth on GaAs. Due to the higher strain in this system, the InGaAs/GaP quantum dots a slightly smaller as compared with In(Ga)As/GaAs ones. Nevertheless, they are optically active based on 0-deminsionally confined electron states. Hence, this new quantum system is promising candidate for the direct integration of III-V based lasers on Si substrate devices.

    2:30 PM - CC2.04

    Observation of Strong Exciton-photon Coupling in ZnO Nanoparticle Based Dielectric Microcavity at Room Temperature

    Xiaoze  Liu1 2, David  Goldberg1 2, Vinod  M.  Menon1 2.

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    ZnO with extremely large oscillator strength and binding energy of 60 meV is an attractive candidate for strongly coupled polariton-based devices operating at room temperature. Here we report room temperature strong-coupling effects in a dielectric microcavity embedded with ZnO nanoparticles. The top and bottom distributed Bragg reflectors (DBR) are fabricated using plasma enhanced chemical vapor deposition and commercially available ZnO nanoparticles in ethanol are sandwiched between the DBRs via spin casting. Results of angle resolved reflectivity and photoluminescence show a Rabi splitting of ~90meV at room temperature. Only the lower polariton branch is observed in the room temperature measurements due to the large Rabi splitting which pushes the upper branch into the scattering and continuum states of ZnO excitons. This agrees well with theoretical coupled oscillator model that takes into account the presence of higher lying scattering and continuum states. It should however be noted that at low temperature (10K), both the polariton branches are clearly observed due to the decrease in homogenous broadening which helps resolve the polariton branches within the scattering and continuum states.

    2:45 PM -

    Break

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    3:15 PM - CC2.05

    Geometry Effects of Linear and Nonlinear Optical Properties in 0D, 1D and 2D II-VI Semiconductor Nanocrystals

    Alexander  Achtstein1, Jonas  Hennig1, Andrei  Schliwa2, Anatol  Prudnikau3, Marya  Hardzei3, Mikhail  Artemyev3, Ulrike  K.  Woggon1.

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    We study optical nonlinearities and exciton-phonon coupling in colloidal 0D to 2D zinc-blende-type (ZB) and wurtzite-type (WZ) semiconductor nanocrystals, i.e. spheres, rods and platelets [1]. Single-particle spectroscopy, temperature-dependent emission and ultrafast recombination dynamics have been measured along with numerical simulations of energy states in 2D-nanosheets which exhibit much narrower ensemble absorption and emission linewidths as compared to colloidal CdSe nanocrystallites ensembles. The observed 2D-heavy hole exciton states show a strong influence of vertical confinement and dielectric screening. A very weak coupling to phonons results in a low phonon-contribution to the homogeneous line-broadening. We present numerical calculations of the 2D-nanoplatelets quantum well exciton energies including Coulomb interaction and compare the obtained energies with experiments. Due to a large surface to volume ratio, the exciton energies show a strong impact of dielectric confinement. Coulomb interaction corrected numerical simulations reproduce this effect. The geometry-dependence of nonlinear optical coefficients (e.g. two-photon absorption coefficient, nonlinear refractive index) is investigated in Z-scan technique and two-photon luminescence excitation (TPLE) measurements. A pronounced change of volume normalized TPA absorption cross sections at the transition from dots to elongated rods has been found. While the bulk TPA coefficient of CdS is 17GM/nm3, it increases in colloidal CdS nanocrystals by more than an order of magnitude depending on shape and size. The contributions of spatial confinement and local field effects of the dielectric environment are evaluated separately to get a deeper insight in the pure confinement effect on TPA. The results from the two different methods, Z-scan and two-photon luminescence excitation (TPLE), show good agreement and confirm the obtained values and size and geometry dependence of the TPA coefficients of dots and rods. The electronic structure of strongly confined semiconductor materials with high nonlinear coefficients makes them ideally suited for two-photon absorption (TPA) based effects, e.g. for 3D optical data storage elements or biological cell imaging. [1] A.W. Achtstein, A. Schliwa, A. Prudnikau, M. Hardzei, M.V. Artemyev, C. Thomsen, U. Woggon Electronic Structure and Exciton−Phonon Interaction in Two-Dimensional Colloidal CdSe Nanosheets, Nano Lett. 12, published online May 24 (2012), DOI: 10.1021/nl301071n

    3:30 PM - CC2.06

    Investigating the Emergent Optical Properties of Gold and Silver Colloidal Superlattices

    Kaylie  Lynn  Young1, Matthew  R.  Jones2, Byeongdu  Lee3, Chad  A.  Mirkin1 2.

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    The ability to create ensembles of inorganic nanomaterials with a high degree of control is of great interest in the development of new materials for applications in various fields including catalysis, optoelectronics, high-density data storage, and biological sensing. Nanocrystal superlattices often exhibit unique electronic, optical, and magnetic properties that are distinct from both the corresponding individual particles and the bulk solid as a result of the interactions between the excitons, surface plasmons, or magnetic moments of assembled particles. In order to study the emergent properties of inorganic nanoparticle assemblies and correlate them to the precise structure of the ensemble, materials-general assembly techniques that allow for tunable lattice parameters are preferred. Consequently, we have explored two methods for synthesizing periodic assemblies of noble metal nanoparticles and have probed their emergent optical properties. Entropic depletion forces, arising from the presence of surfactant micelles, have been utilized to assemble anisotropic nanoparticles into one-, two-, and three-dimensional superlattices in solution with anomalously large lattice parameters. The effects of surfactant concentration, temperature, ionic strength, and colloid size on interparticle spacing have been investigated. In a complementary approach, DNA has been used as a programmable linker to assemble gold and silver spherical nanoparticles into superlattices with a variety of crystallographic symmetries ranging from face-centered cubic (FCC) and body-centered cubic (BCC) to more complex arrangements such as AB2, AB3, and AB6. The lattice parameters of these superlattices can be adjusted with nanometer precision, as shown by synchrotron small angle X-ray scattering (SAXS). The surface plasmon resonance (SPR) of the nanoparticle superlattices can be tuned across the visible range by controlling the interparticle spacing and crystallographic arrangement. Furthermore, the assemblies of anisotropic nanoparticles exhibit blue-shifted plasmon resonances compared to the red-shift that occurs for assembled spherical nanoparticles.

    3:45 PM - CC2.07

    Induced Chiroptical Activity in Colloidal Quantum Dots

    Assaf  Ben-Moshe1, Gil  Markovich1.

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    The property of induced chiroptical activity was studied in type II-VI semiconductor quantum dots [1]. Different mechanisms for induction were evaluated in light of experimental nanoparticle size and material dependence laws derived in this work. Circular dichroism (CD) and fluorescence detected circular dichroism (FDCD) are used to study the electronic level structure of quantum dots revealing information which is not detected by conventional absorption spectroscopy. It is shown that induction mechanisms working in achiral nanocrystals only lead to very weak effects. A new concept is suggested to enhance the optical activity of nanoscale chiroptically active materials, relying on chiral crystallization of inorganic nanocrystals. This demonstration connects the fundamental work of Pastuer dating as early as the 19th century to nanoscale science for the first time. Huge chiroptical effects were measured in enantiopure samples of nanocrystals of the chiral phase of mercury sulfide (cinnabar). These were obtained by a new synthetic approach which enables control of chirality of the nanocrystals which are formed in a colloidal synthesis. Unique properties are revealed in this newly introduced system such as intriguing dependence of chiroptical activity on shape and crystallinity. This approach is expected to set the ground for a new field of materials science with a variety of applications. Finally, the non linear optical properties of these nanocrystals have been studied, revealing very strong second harmonic generation activity. [1] Ben Moshe, A.; Szwarcman, D.; Markovich, G. "Size Dependence of Chiroptical Activity in Colloidal Quantum Dots" ACS Nano, 2011, 5 (11), 9034-9043.

    4:00 PM - CC2.08

    Electrically Conductive, Crack-free Nanopatterned Films of Semiconductor Nanocrystals Reveal Higher Conductivity and Unusual Current NoiseA

    Tamar  Shoshana  Mentzel1.

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    We present the first semiconductor nanocrystal films of nanoscale dimensions that are electrically conductive and crack-free. These films make it possible to study the electrical properties intrinsic to the nanocrystals unimpeded by defects such as cracking and clustering that typically exist in larger-scale films. Our technique for forming the nanoscale films is based on electronbeam lithography and a lift-off process. The patterns have dimensions as small as 30 nm and are positioned on a surface with 30 nm precision. We achieve unprecedented versatility in integrating semiconductor nanocrystal films into device structures both for studying the intrinsic electrical properties of the nanocrystals and for nanoscale optoelectronic applications. We find that the electrical conductivity of the nanoscale films is 180 times higher than that of drop-cast, microscopic films made of the same type of nanocrystal. In the nanoscopic patterns, we find additional noise in the current that is thermally activated. This noise is unusual in that it is of a comparable order of magnitude to the average current, and we find switching behavior where the average current changes by an order of magnitude in time. This noise cannot be explained by commonly known origins of current noise, and thus we believe that we are observing a novel effect in the nanocrystals.

    4:15 PM - CC2.09

    Non-resonant Photoluminescence Enhancement in Hybrid Metal-semiconductor QW Systems

    Antonio  Llopis1, Jie  Lin1, Karol  Gryczynski1, Sergio  Pereira2, Ian  M  Watson3, Greg  Salamo4, Arkadii  A  Krokhin1, Arup  Neogi1.

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    Among other uses, plasmonics is currently being investigated to improve the efficiency of solid-state light emitters. Coupling to surface plasmons gives rise to a sharp increase in the density of radiative e-h states near plasmonic resonance (so-called Purcell factor). This increase leads to strong enhancement of spontaneous emission, as has been previously observed in photoluminescence (PL) experiments on various hybrid metal/semiconductor (M/SC) systems. Plasmonically enhanced light emitting devices, however, comprise only a subset of all possible hybrid M/SC systems. We demonstrate here that PL enhancement can be achieved in non-resonant hybrid M/SC structures, that the enhancement is strongly localized around the metal nanoparticles, and that it is accompanied by experimental features which clearly differentiate it from resonant (plasmonic) enhancement. Results are presented for two hybrid M/SC systems: An InGaN/GaN MQW with embedded Au NPs, and a GaAs/AlGaAs QW with Ga nanodroplets deposited on the surface. Despite having differing geometries and emission wavelengths, we demonstrate that both systems exhibit localized enhancement in the vicinity of the NPs, and that this occurs in the absence of resonant plasmonic interaction. In addition, the systems share two additional important experimental features: An increase in the PL decay time and power-dependent intensity saturation. Using a simple, but comprehensive, model which takes into account the electrostatic effects of the metal NPs on the electron-hole kinetics within the QW, we are able to explain the origin of the localized enhancement and duplicate the observed experimental features. This demonstrates that the enhancement arises due to electrostatic interaction with the NPs. This method for emission enhancement should be easily applicable to nano-scale light emitters over a wide-range of emission wavelengths due to its non-resonant nature.

    4:30 PM - CC2.10

    Record-brightness of Infrared Colloidal Quantum-dot LEDs through Control of the Exciton Dynamics

    Liangfeng  Sun1 5 2, Joshua  J.  Choi3 2, David  Stachnik2, Adam  Bartnik2, Byung-Ryool  Hyun2, George  Malliaras4, Tobias  Hanrath3, Frank  W.  Wise2.

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    Colloidal quantum dots (QDs) are promising materials for various optoelectronic device applications by virtue of their size- and shape-tunable optical and electronic properties. There is great interest in the development of low-temperature solution processing of QD devices, for next-generation photovoltaics, photodetectors and light emitting diodes (LEDs). The central issue in the physics of optoelectronic devices based on nanostructured materials is the control of charge-carrier dynamics. However, manipulation of the excitons in these materials remains a significant challenge, and consequently device performance has been limited. In our research, we demonstrated that the electronic coupling between the adjacent QDs can be dramatically varied by tuning the spacing between them. A variation of a few angstroms in the spacing results in a few orders of magnitude change in exciton dynamics - recombination and dissociation. The LEDs based on PbS QDs have reached record-brightness. The radiance is an order of magnitude higher than in previous QD LEDs. The maximum external quantum efficiency of the LEDs is about 2%. These solution-processed LEDs can be fabricated to emit over the range 800 ~ 1850 nm and compete with the performance of state-of-the-art infrared LEDs fabricated by planar epitaxial technology over the range 900 ~ 1300 nm [Nature Nanotechnology 7, 369-373 (2012)].

    4:45 PM - CC2.11

    Efficiency `Drooping’ in `Hybrid’ Organic-inorganic Colloidal Quantum-dot Light-emitting Diodes

    Yasuhiro  Shirasaki1, Geoffrey  J.  Supran*1, Katherine  W.  Stone1, William  A.  Tisdale1, Vladimir  Bulovic1.

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    We describe spectroscopic measurements of the electroluminescence (EL) and photoluminescence (PL) of quantum dots (QDs) in biased high performance quantum dot light-emitting diodes (QD-LEDs), which allow us to deduce that the origin of the efficiency roll-off commonly observed at high voltages is a reversible electric-field-induced quenching of QD PL quantum yield (QY). To do so, we first devised a method for the simultaneous and non-perturbative measurement of QD PL QY and QD-LED external quantum efficiency (EQE) during active device operation. The PL QY of the QDs is seen to rapidly decrease above 4V and to track the roll-off (‘drooping’) of the EQE. To our knowledge, this is the first direct demonstration that the QD layer is responsible for the efficiency ‘droop’ in QD-LEDs, and that this is a result of the quenching of QD PL at high biases. Red-shifting of EL spectra, which we assign to the quantum-confined Start effect (QCSE), suggests that this PL quenching may be a result of electric-field-induced polarization of excitons generated within the QD film. To test this hypothesis, we isolated the impact of electric-field from other potential culprits, such as charge-induced Auger recombination, by monitoring the red-shifting and quenching of QD PL in a reverse biased QD-LED. Using the QCSE as a signature of local electric-field, the bias dependence of the EQE was predicted and found to be in excellent agreement with the efficiency ‘drooping’ observed in our forward biased devices. This allows us to conclude that electric-field alone is indeed responsible for QD PL quenching, and, in turn, EQE ‘drooping’ in our QD-LEDs. Further more, electroabsorption measurements of these QD-LEDs, which also exhibit the QCSE and suggest negligible QD charging, corroborate our findings. The ‘hybrid’ QD-LED investigated here, comprising organic and inorganic charge transport layers, represents the latest generation of device architecture. This study therefore informs the design of QD-LEDs with improved efficiencies at the high current densities required for high-brightness devices.

    CC3: Poster Session: Optical Materials and Devices I

    • Monday PM, November 26, 2012
    • Hynes, Level 2, Hall D
     

    8:00 PM - CC3.01

    Next-generation Nanocrystals for Imaging: Non-bleaching, Non-blinking, Anti-stokes Phosphors

    Bruce  E  Cohen1.

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    Single-particle studies of phosphorescent lanthanide-doped upconverting nanoparticles (UCNPs) have shown that they exhibit nearly ideal properties as single molecule imaging probes. UCNPs absorb two photons in the near infrared and emit one at shorter wavelengths in the visible or nIR, an unusual characteristic that distinguishes them from all luminescent molecules in the cell, and one that suggests background-free cellular imaging. We have shown that UCNPs do not blink on and off as most other probes do, and that they posses remarkable photostability, resisting photobleaching under continuous irradiation long after organic dyes, proteins, and even quantum dots are extinguished. The promise of these nanoparticles has been tempered by difficulties in controlling nanoparticle size, emissive color, and in fully characterizing their optical properties. We have recently developed synthetic methods for control of UCNP size, down to GFP-sized nanoparticles, and methods for characterizing quantum yields, lifetimes, and single molecule emissions. A combinatorial lanthanide scan has allowed us to tune emission and excitation wavelengths for extended, multicolor, single- or dual-particle tracking. Finally, we are developing simple, protein-based coatings to passivate the nanocrystals and permit straightforward methods for nanocrystal immunotargeting.

    8:00 PM - CC3.03

    Optical Properties of Au-Ag Core-shell Nanorods and Their Chemical/Electrochemical Reactions

    Yasuro  Niidome1 2, Yukiko  Tsuru1, Yuki  Hamasaki1, Naotoshi  Nakashima1 2 3.

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    Anisotropic metal nanoparticles have been an attractive research target because of their remarkable spectroscopic properties. We have reported Au-Ag core-shell nanorods of which spectroscopic properties corresponded to those of anisotropic silver nanoparticles [1-4]. Our core-shell nanorods were uniform in their shapes and showed four peaks in their extinction spectra. We evaluated extinction spectra of the Au-Ag core-shell nanorods on a plate in changing the incident angles of the monitor light. The spectral changes depending on the incident angles were helpful to discuss the origins of the bands in the extinction spectra. Deconvolution of the spectra indicated that six bands made an extinction spectrum. The peak locating in the longest wavelength regions (650 nm) was assigned to aggregates of the nanorods. The second longest peak (500 nm) could be assigned to the longitudinal SP band of the nanorods. The changes of the other four peaks were complicated, but two of them were assigned to be parallel (420 nm) and perpendicular (380 nm) transitions against the plate surface. Chemical and electrochemical oxidation can dissolve the silver shells on a plate. The oxidation of silver shells induced dramatic spectroscopic changes. The spectroscopic changes indicated how the silver shells were oxidized. In the case of the electrochemical oxidation, the core-shell nanorods were deposited on an ITO plate, and in-situ spectroscopy was performed during cyclic voltammogram measurements. The in-situ observation showed the characteristics of the oxidation and reduction processes of silver shells. [1] Y. Tsuru, N. Nakashima, Y. Niidome, Optics Commun. (in press). [2] M.R. Cortie, F. Liu, M.D. Arnold, Y. Niidome, Langmuir (in press). [3] L. Wang, A. Kiya, Y. Okuno, Y. Niidome, N. Tamai, J. Chem. Phys. 134 (2011) 054501. [4] Y. Okuno, K. Nishioka, A. Kiya, N. Nakashima, A. Ishibashi, Y. Niidome, Nanoscale 2 (2010) 1489.

    8:00 PM - CC3.04

    Dynamic Fluctuations in Ultrasmall Nanocrystals Induce White Light Emission

    Timothy  J  Pennycook1 2 5, James  R.  Mcbride3, Sandra  J  Rosenthal3 1 2, Stephen  J  Pennycook2 1, Sokrates  T  Pantelides1 2 4.

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    As the size of semiconductor nanocrystals has been pushed to their lower limits to fully exploit quantum confinement, new properties have emerged. Nanocrystals that display size-tunable monochromatic emission when small, emit across a broader range of energies when their size is reduced into the ultrasmall sub-2nm range [1]. White-light emission from ultrasmall CdSe nanocrystals is a particularly interesting case of such broad emission because of its potential for solid-state lighting [2,3]. The white light consists of a continuum of emission energies spanning the visual range. Experiments have ruled out a broad distribution of sizes as the cause, and have shown that individual ultrasmall CdSe nanoparticles emit white light. We have investigated small to ultrasmall CdSe nanocrystals using a combination of state-of-the-art scanning transmission electron microscopy and finite-temperature quantum molecular dynamics simulations. Our findings indicate that following excitation, partial thermalization sets the ultrasmall nanocrystals into a disordered fluxional state. These dynamic fluctuations cause the band gaps of the ultrasmall nanoclusters to vary continuously across the visual range on a femtosecond time scale. When averaged over time, transitions across all these different band gaps fill the visual spectrum and produce the white light. Furthermore, although the larger monochromatic emitting nanocrystals we have observed possess stable crystal cores, their surfaces are fluxional. Dynamic fluxionality should be taken into consideration when optimizing nanocrystals for applications. Research at Vanderbilt was supported in part by the U.S. Department of Energy Grant DE-FG02-09ER46554 (TJP, STP) and the McMinn Endowment (STP). Research at Oak Ridge National Laboratory was sponsored by the U.S. Department of Energy, Office of Science, Materials Sciences and Engineering Division (SJP). Computations were performed at the National Energy Research Scientific Computing Center at Lawrence Berkeley National Laboratory. [1] Landes, C. F., Braun, M. & El-Sayed, M.A. On the nanoparticle to molecular size transition: fluorescence quenching studies. J. Phys. Chem. B 105, 10554-10558 (2001). [2] Bowers II, M.J., McBride, J.R. & Rosenthal, S.J. White-light emission from magic-sized cadmium selenide nanocrystals. J. Am. Chem. Soc 127, 15378-15379 (2005). [3] McBride, J.R., Dukes III, A.D., Schreuder, M.A. & Rosenthal, S.J. On ultrasmall nanocrystals. Chem. Phys. Lett. 498, 1-9 (2010).

    8:00 PM - CC3.05

    Pattern Transfer of Inorganic Nanostructures on Glass by Using Nanoimprint Films

    Chia-Lung  Lee1, Toshiyuki  Mihara1, Masaru  Yamashita1, Tomoko  Akai1.

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    In recent years, periodic nanostructures at the substrate/air interface have attracted considerable attention in the field of optoelectronic devices because of their good performance in improving light extraction. To date, the direct formation of periodic nanostructures onto glass is achieved by nanoimprint lithography (NIL). However, it is difficult to obtain large-area periodic nanostructures on the surface of glass by NIL. To fabricate inorganic periodic nanostructures onto glass, in this work, we report a novel method of pattern transfer by using nanoimprint films. A nanoimprint film having a hole pattern is employed as a template, which achieves a periodic arrangement of inorganic nanostructures. After filling silica beads into the hole pattern or applying a sol-gel solution to the surface of film, the hole pattern side of film is then placed face downward in contact with the glass substrate and held in place by a weight. After a pattern transfer process, it is found that the periodic inorganic nanostructures were successfully transferred from the nanoimprint film onto the surface of the glass substrate. Various arrangements of inorganic nanostructures can be easily fabricated by using hole patterns with different intervals and arrangements. Our findings indicate that this pattern-transfer method is a promising candidate for the inexpensive fabrication of large-area periodic nanostructures onto glass. We consider that this method of pattern transfer has potential applications in lighting equipment and optoelectronic devices.

    8:00 PM - CC3.06

    Rational Synthesis of Monodisperse Metal Sulfide Colloidal Nanocrystals Using (NH4)2S as a Sulfide Precursor

    Haitao  Zhang1, Byung-Ryool  Hyun2, Christian  Ocier1, Frank  W.  Wise2, Richard  D.  Robinson1.

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    Tremendous efforts have been made on the synthesis of metal chalcogenide nanocrystals (NCs) in the last 30 years due to their size-tunable spectroscopic properties. The pioneering work on monodisperse metal sulfide colloidal NCs synthesis by the Bawendi group in 1993 used elemental sulfur as a sulfide precursor. This elemental sulfur precursor has subsequently been widely applied to the synthesis of metal sulfide NCs. In general, the elemental sulfur (S0) has to be reduced to S2- before bonding to metal cation. The molecular mechanisms involved in this process, however, remain complicated and unclear. The lack of a rational synthetic method has caused many complications in metal sulfide colloidal nanocrystal synthesis, such as unreproducible products and low conversion yield. The stoichiometric reaction between (NH4)2S and metal salts affords a rational synthetic method to metal sulfides. Due to its poor solubility in nonpolar solvents, (NH4)2S has been mainly used as a reagent in aqueous phase nanocrystal synthesis, which generally yields low quality particles with wide size distributions. Here we describe the first use of (NH4)2S as a generic sulfide precursor in organic nonpolar-phase nanocrystals synthesis. Our novel method has produced a variety of monodisperse metal sulfide colloidal nanocrystals, including CdS, Ag2S, Bi2S3, SnS, Cu2S, ZnS, and MnS. The stoichiometric reaction between (NH4)2S and metal salts can produce metal sulfide nanocrystals with high conversion yield, and more than 30g monodisperse nanocrystals can be synthesized in a single reaction. (NH4)2S exhibits very high reactivity at relatively low temperatures, which provides new opportunities to synthesize small size quantum dots that are difficult to be obtained by the conventional high temperature methods. This work was supported in part by the National Science Foundation under agreement DMR 1120296.

    8:00 PM - CC3.08

    Hybrid Systems from J-aggregates and Inorganic Nanowires - A Study by Transmission Electron Microscopy (TEM) and Cryogenic TEM

    Frank  Polzer1, Egon  Steg1, Yan  Qiao1, Holm  Kirmse1, Stefan  Kirstein1, Jürgen  P.  Rabe1.

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    One-dimensional inorganic nanostructures have attracted huge interest because of their promising properties for electronics, plasmonics and sensing applications. One approach for the synthesis of these systems is solution-based, template-directed growth using surfactants, block-co-polymers etc. It was shown recently that silver nanowires can be grown within tubular J-aggregates of amphiphilic cyanine dye molecules1. These inorganic nanowires are grown by reduction of silver salt in aqueous solution and show a diameter around 7 nm with a length up to several micrometers. A detailed structural characterization of the hybrid inorganic-organic system requires complete analysis from the atomic scale to the micrometer scale. Transmission electron microscopy (TEM) provides various tools for structural and chemical characterization, such as HRTEM/STEM, electron diffraction and analytical methods for the inorganic part of the hybrid system, and cryogenic TEM (cryoTEM) as an outstanding method for imaging the organic part. CryoTEM allows in-situ imaging of frozen hydrated samples in their native state and was successfully applied to biological samples but also to hybrid materials in solution.2 To maintain their native state, the samples are plunge-frozen into a suitable cryogen (here liquid ethane at ca. -183 °C), resulting in the material becoming embedded in a thin layer of vitreous ice. The TEM imaging under these cryo-conditions avoids damages of the soft organic material under high vacuum conditions. In the case of the hybrid materials from J-aggregates and inorganic nanowires, cryoTEM was applied to follow the growth of the silver nanowires at different time steps. From the images information about the nucleation and growth mechanism of the nanowires within the self-assembled aggregates is deduced. In combination with results from TEM a first model for the growth of the nanowires within the J-aggregates can be presented here. References: 1 Eisele D. M. et al., J. Am. Chem. Soc. 2010, 132, 2104. 2 Nudelmann et al., Soft Matter 2011, 7, 17.

    8:00 PM - CC3.09

    InP Core/Shell Heterostructured Nanocrystal Quantum Dots: Suppressing Blinking into the NIR

    Allison  M  Dennis1, Benjamin  D  Mangum1, Andrei  Piryatinski2, Han  Htoon1, Jennifer  A  Hollingsworth1.

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    Many fluorophores, including organic dyes, fluorescent proteins, and nanocrystal quantum dots (NQDs), exhibit fluorescence intermittency, or blinking.(1) Recent experiments demonstrate that judicious core/shell heterostructuring of NQDs yields significantly suppressed blinking through either interfacial alloying or thick shelling.(2,3) Concurrent suppression of non-radiative Auger recombination (AR) has also been established with important implications for low-threshold multi-color lasing and efficient multiexciton emission.(2,4) Expanding beyond limited CdSe-based examples of core/shell engineering, we explore thick-shell heterostructuring of InP NQDs. The effect of shell composition and thickness on NQD photophysical properties is explored by applying thick shells of four different materials (ZnS, ZnSe, CdS, and CdSe) to InP cores. Of the four distinct heterostructures synthesized, InP/CdS and InP/CdSe exhibit a type-II bandgap structure, which affords complete spatial separation of excited-state carriers and red-shifts excitonic emission into the near-infrared, while InP/ZnS and InP/ZnSe exhibit type-I and some limited quasi-type-II behavior, maintaining emission in the visible wavelength range. Among other results, we found that InP/CdS NQDs exhibit suppressed blinking and AR (indicated by long biexciton lifetimes), similarly to their thick-shell CdSe/CdS (“giant” NQD, g-NQD) counterparts; unlike the earlier system, however, blinking suppression is not strictly confined to thick shells. Significantly, room-temperature blinking behavior for a fully type-II system has not been previously demonstrated as attempts have been thwarted by extreme sensitivity to photobleaching and low signal-to-noise at the single-dot level, making our result the first example of both a non-blinking NQD emitting in the NIR and a non-blinking type-II NQD.(5) The long biexciton lifetime of the thick-shelled InP/CdS NQDs shows promise for amplified spontaneous emission (ASE), while core/shell/shell materials that sequester cadmium (i.e., InP/CdS/ZnS) have applications in tissue imaging. As the synthesis of these four heterostructures is optimized, more information is gathered about the interplay between electronic structure, core and shell dimensions, and photophysical properties, including the emission wavelength, quantum yield, fluorescent lifetime, biexciton lifetime, blinking, and photostability. This body of knowledge enables us to design NQD heterostructures for a range of applications from lasing to photonics to biomedical imaging. 1. Chemphyschem 2007, 8, 823; Nature 1997, 388, 355; J Chem Phys 2000, 112, 3117; Nano Lett 2001, 1, 557. 2. Nature 2009, 459, 686. 3. JACS 2008, 130, 5026; J Biophotonics 2010, 3, 706; Nat Mater 2008, 7, 659; Phys Rev Lett 2009, 102, 136801. 4. Nano Lett 2009, 9, 3482; Nano Lett 2010, 10, 2401. 5. J Phys Chem C 2011, 115, 436.

    8:00 PM - CC3.10

    Synthesis and Characterization of Luminescent SiC Tetrapods

    Andrew  P.  Magyar1, Igor  Aharonovich1, Mor  Baram1, Evelyn  L  Hu1.

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    Recent advances in the synthesis of nanoscale structures have extended to the formation of 3D structures of higher complexity than nanowires or quantum dots. For example, the highly symmetric branched structure and nanoscale geometry of the ‘tetrapod’ is known to yield unique optical and electronic properties enabling the exploitation of these structures for applications including photovoltaics, scanning probe microscopy, and bio-labeling. Tetrapods have been formed in a variety of materials, primarily II-VI semiconductors such as ZnO, CdTe and ZnS. In this work, we report of the formation of silicon carbide tetrapod-shaped nanostructures synthesized via microwave-assisted plasma chemical vapor deposition. While the possibility of SiC tetrapods has been theoretically predicted, to the best of our knowledge, this is the first report of the synthesis of SiC tetrapods. The growth of the tetrapods is seeded from adamantane embedded in a silica sol-gel matrix. Our adamantane-seeded CVD growth of SiC is a facile approach for the formation of tetrapods, requiring no sophisticated chemical syntheses. The tetrapods were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and microphotoluminescence spectroscopy. The average size of the tetrapods can be controlled from between ~10 nm to ~150 nm arm to arm by tuning the growth conditions. Remarkably, however, the size distribution is uniform for an individual set of conditions. TEM confirms that the tetrapod nanoparticles synthesized in this work are SiC, having a zinc-blende (3C) core and wurtzite (4H) arms, in accord with the suggested model for SiC tetrapods. The tetrapods exhibit room temperature photoluminescence (PL). The emission wavelength of the PL is sub-band gap for SiC. The emission maximum varies for different tetrapods, appearing between 550 nm and 800 nm with a FWHM of ~5 nm. The mechanical strength and chemical stability of SiC coupled with the unique nanoscale structure of the tetrapod and their room temperature photoluminescence enables potential applications in photonics, biolabeling and sensing.

    8:00 PM - CC3.11

    Synthesis and Characterization of TiO2 Nanoparticles with a Large Percentage of Reactive (001) Surface

    Zhenquan  Tan1 2, Tsutomu  Tanaka1, Chiaki  Ogino1, Akihiko  Kondo1, Satoshi  Ohara2.

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    The anatase TiO2 is generally synthesized with crystal facets dominated by thermodynamically stable (101) surface rather than chemically reactive (001) surface. Recently, synthesis of anatase TiO2 with a large percentage of (001) surface is of great research interests because it has great potential in applications such as high performance catalyst, fuel cell, and chemical sensors. In this study, we report a simple hydrothermal approach for the synthesis of anatase TiO2 nanoparticles having (001) surface. A lowly toxic ammonium hexafluorotitanate (IV) is used as the Ti precursor instead of the highly hazardous hydrofluoric acid. The as-prepared TiO2 nanoparticles have a square shape and contribute to a large percentage of reactive (001) surface. The unique structures and the optical properties were characterized by SEM, TEM, XRD, Raman Spectroscopy and UV-Vis absorption spectroscopy.

    8:00 PM - CC3.12

    Influence of N-doping on the Properties of TiO2 Nanoparticles Synthesized by Laser Pyrolysis and Application to Solid-state Dye-sensitized Solar Cells

    Nathalie  C  Herlin Boime1, Hussein  Melhem2, Catherine  DiBin2, Bernard  Ratier2, Pardis  Simon1, Yann  Leconte1, Malgorzata  Makowska-Janusik4, Adi  Kassiba3, Johann  Boucle2.

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    Titanium oxides are intensively exploited in the field of photo-catalysis or photovoltaic energy conversion, due to their relevant physical properties, their non-toxicity and their relatively cheap synthesis. In particular, dye-sensitized solar cells (DSSC) based on nanocrystalline TiO2 electrodes demonstrate high power conversion efficiencies over 12%, which allowed the emergence of commercial products developed at low costs, as alternative to inorganic solar cells. However, although many research efforts have been devoted to identify alternative metal oxides or alternative electrode architectures, anatase TiO2 processed from colloidal pastes remain the material of choice to achieve the best performance up to now. Further development of DSSC will require the demonstration of novel device concept that may exploit additional charge generation mechanisms. In this context, several attempts are reported towards the doping of anatase TiO2 with transition elements in order to tune its electronic and optical properties. In particular, nitrogen-doping was used as a relevant strategy to reduce the optical band gap of the metal oxide, while improving the charge kinetics in DSSC (reduced recombination, improved charge transport). Although improved device performance is observed, only partial interpretations of the underlying mechanisms are given. In this work, we investigate the electronic properties of TiO2 and N-doped TiO2 nanocrystals synthesized by laser pyrolysis and used as building blocks for solid-state dye-sensitized solar cells. By exploiting both electron paramagnetic resonance analysis and numerical simulations, of the titanium oxide structure, we discuss the influence N-doping on the electronic and optical properties of the nanopowders, and we emphasize the role of ambient oxygen and light on their features. The photovoltaic performance of the corresponding devices is also discussed with regard to these elements.

    8:00 PM - CC3.14

    In situ Formation and Photo Patterning of Emissive Quantum Dots

    Ashu  Kumar  Bansal1, Francesco  Antolini2, Lenuta  Stroea2, Tomas  Kasponas3, Gediminas  Raciukaitis3, Andreas  Hirzer4, Volker  Schmidt4, Sybille  Allard5, Ullrich  Scherf5, Ifor  Samuel1.

    Show Abstract

    Nanostructured composites of inorganic and organic materials are attracting extensive interest for electronic and optoelectronic device applications. Here we report a novel method for the fabrication of metal selenide nanoparticles in organic semiconductor films that is compatible with solution processable large area device manufacturing. Our approach is based upon the controlled in situ thermal decomposition of cadmium selenide precursor complex in a film of the electron transporting material 1,3,5-tris(N-phenyl-benzimidazol-2-yl)-benzene (TPBI). Specifically we show that the photoluminescence quantum yield (PLQY) of the thermally converted CdSe quantum dots (QDs) in the TPBI film is up to 15%. The PLQY depends on the concentration of the solution, blend ratio of the precursor and the annealing temperature. Time-resolved photoluminescence studies show the fast energy transfer from the organic host to the emissive QDs. The results emphasize the importance of the alignment of energy levels between the host and guest dopants. We also show that laser irradiation can form the QDs from the precursor. This is an important result as it enables direct laser patterning (DLP) of the QDs. The DLP is performed on these blends with a picosecond laser at 266 nm wavelength at various irradiation doses. The confocal microscopy reveals the formation of the emissive QDs after laser processing. The optical and structural properties of the QDs are also analysed by means of UV-Vis, PL spectroscopy and transmission electron microscopy (TEM). The results show that the QDs are well distributed across the film and their emission can be tuned over a wide range by varying the temperature or laser power used on the blend films. Our findings provide a route to the low cost patterning of hybrid electroluminescent devices.

    8:00 PM - CC3.15

    Three Dimensional Poly(3,4-ethylenedioxythiophene) Nanostructures for Infrared Electrochromic Devices

    Bumsoo  Kim1, Jerome  Kartham  Hyun1, Seokwoo  Jeon1.

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    Three dimensional (3D) poly(3,4-ethylenedioxythiophene) (PEDOT) can be useful for infrared (IR) electrochromic devices which exhibits reversible changes of the refractive index upon doping in mid to long-infrared regime (3-5 µm, 8-12 µm) at low operational voltages (< 3 V). The difference in optical properties between the doped and undoped states of PEDOT can be enhanced and engineered by structuring PEDOT in the form a 3D photonic crystal. However the realization of 3D PEDOT has not yet been demonstrated. Here we present successful infiltration of PEDOT into 3D silica colloidal crystal templates by electropolymerization. Preliminary optical results show that 3D PEDOT improves the absorbance by 150% relative to that of a planar film for IR wavelengths. The contrast in IR transmission between doped and neutral states of 3D PEDOT is further enhanced. Moreover, the larger surface area from 3D structures compared to that of a planar film significantly reduces the switching time to less than 1 second by increasing the efficiency of electrochromic processes.

    8:00 PM - CC3.17

    Incorporation of Luminescent Zinc Oxide Nanoparticles into Polystyrene

    Rui  Li1, Robert  Withnall1, Jack  Silver1, Peter  Bishop2, Weiliang  Wang2.

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    Many polymers degrade in-service due to exposure to near ultraviolet light. Such degradation can involve photo-oxidation reactions that proceed via free radical mechanisms causing polymer chain scission and branching. In this work, zinc oxide (ZnO) nanoparticles were synthesised by flame spray pyrolysis. The nanoparticles were then fired in a reducing atmosphere to produce luminescent zinc oxide (ZnO:Zn) particles. Both the as-prepared ZnO and the reduced ZnO:Zn nanoparticles were well characterised by means of X-ray diffraction, dynamic light scattering and laser Raman spectroscopy. A transparent polystyrene composite sheet incorporating reduced ZnO:Zn nanoparticles was produced using a solvent casting method. The composite sheet had comparable transmission to a virgin polystyrene film. This was achieved by uniformly dispersing the ZnO:Zn nanoparticles into the polystyrene, as is made evident by SEM images and optical micrographs. The photoluminescent characteristics of the ZnO:Zn, both as a pure powder and embedded in a polystyrene matrix, are reported. The ZnO:Zn pure powder can absorb broadly across nearly the entire near ultraviolet range and emit bright green light. The polystyrene host does not inhibit either the absorption or the emission of the ZnO:Zn. The uniformity of the photoluminescence of the composite sheet under near ultraviolet excitation is reported. The luminescent ZnO:Zn nanoparticles therefore have applications for use not only as an inhibitor of the ultraviolet degradation of polymers, but also for providing polymers with light emitting functionality.

    8:00 PM - CC3.19

    Impact of Photo-induced Processes on the Plasmonic Enhancement of Colloidal Quantum Dot Emission

    Seyed  M  Sadeghi1 2, Robert  G.  West1.

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    The narrow emission spectra, tunabilitiy, and high quantum yields of colloidal quantum dots (QDs) have made them quite appealing candidates for various applications, including fluorescence probes for biomolecular and in vivo analytical applications, light emitting diodes, solar cells, etc. Currently significant research efforts are being devoted towards utilizing the plasmonic properties of metallic nanoparticles (MNPs) to improve the optical properties of QDs and envision new applications, such as active nanoparticle systems, nanothermometers, biological and chemical sensors, etc. A main feature of colloidal QDs, however, is that when they are irradiated, their fluorescence and physical structures can change significantly. This includes photo-induced processes which increase their emission efficiencies (photoinduced fluorescence enhancement) and photo-oxidation which can suppress their emission wavelengths and intensities. In this contribution we discuss the impact of such photoinduced processes (or light irradiation) on the plasmonic enhancement of emission of close packed CdSe/ZnS colloidal quantum dots when they are in the vicinity of gold metallic nanoparticles. Since in our samples QDs can interact with each other, our results reveal the interplay between QD interdot interaction and plasmonic effects. In this investigation, we vary the MNP sizes and laser intensities to examine how such an interplay is influenced by the heat generated by MNPs and their plasmonic field strengths. Our results outline the strong dependency of plasmonic emission enhancement of QD solids on the exciting light intensity. Therefore, these results are important for the diverse on-going research involving colloidal QDs and plasmonic effects.

    8:00 PM - CC3.20

    Colloidal Hybrid Nanostructures: A New Type of Bifunctional Materials

    Murat  Kaya1, Serap  Kaya2, Murvet  Volkan3.

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    Magnetic nanoparticles have potential applications in magnetic separation, tissue imaging, drug delivery, and information storage. Therefore their synthesis has scientific and technological interest. Recently, incorporation of metallic gold onto magnetic nanoparticles makes the core/shell composite nanoparticles extremely interesting for magnetic, optical, and biomedical applications due to their plasmonic properties, stabilizing effect toward corrosive biological conditions and well known Au-S chemistry which permits the easy functionalization of the surface. In this work, we have fabricated silica coated magnetic cobalt nanospheres decorated with gold nanoparticles (Co-SiO2-Au ). These magnetic and optical bifunctional nanoparticles take advantage of the strong resonance absorption for SERS studies and easy separation via external magnetic field. The performance of the prepared gold nanoparticles attached magnetic silica spheres as SERS substrate was evaluated using brilliant cresyl blue (BCB), rhodamine 6G (R6G) as model compound. The SERS detection of 4-mercapto benzoic acid (4-MBA) from aqueous solutions using bifunctinal Co-SiO2-Au nanoparticles were also investigated.

    8:00 PM - CC3.21

    A Facile Synthesis of Gold Rhombic Dodecahedra via Seeded Growth with Well-controlled Sizes and Their Optical Properties

    O Ok  Park1 3, Choi  Kyeong Woo1, Do Youb  Kim1, Sang Hyuk  Im2.

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    We present a facile method for the synthesis of uniform Au rhombic dodecahedra via seeded growth with well-controlled sizes and optical properties. We could reproducibly obtain Au rhombic dodecahedra with a narrow size distribution (<5% in standard deviation) and in high percentage (>90%). In order to synthesize Au rhombic dodecahedra with uniform in shape, controllable sizes, and in high percentages, N,N-dimethylformamide (DMF), which can stabilize {110} facets of Au nanocrystals, was adopted both as a solvent and a reducing agent to a seed-mediated growth method, which could offer great flexibility in controlling both the shape and the size of the nanocrystals, using single-crystal Au nanocrystals with uniform in shape and size as seeds. Meanwhile, since only poly(vinyl pyrrolidone), a common stabilizer for nanocrystals, in the growth system using DMF often resulted in the formation of Au nanocrystals enclosed by {111} facets, trisodium citrate was additionally introduced in the present system as a stabilizer for the formation of Au rhombic dodecahedra. Moreover, size of uniform Au rhombic dodecahedra can be systematically controlled over a wide range and each size of Au rhombic dodecahedra was selectively synthesized in high percentage. The edge lengths of these Au rhombic dodecahedra could be readily controlled from 19 to 67 nm in a controllable fashion by varying the amount of seeds or concentration of HAuCl4, or both. The corresponding localized surface plasmon resonance peak positions of the Au rhombic dodecahedra could be continuously shifted from 532 to 655 nm depending on their sizes. The uniform shape and size of the Au nanocrystals allowed us to gain better understanding of the effects of various reaction parameters on the evolution of nanocrystals, including water contents, concentration of trisodium citrate, and reaction temperture.

    8:00 PM - CC3.22

    Surfactant-free Synthesis of Ultrafine Au Nanoparticles on CdS Nanorods by Controlled Heterogeneous Nucleation

    Subhajit  Kundu1, Paromita  Kundu1, N.  Ravishankar1.

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    Semiconductor-metal heterostructures form an important class of materials as they are useful in photocatalytic, labeling and other optical applications. For enhanced property there is a need for cleaner surface as it promotes facile electron transport. Physical deposition methods are useful in creating such clean surfaces but controlling particle size and uniformity is difficult to achieve. However, by wet-chemical methods control of particle size is good and uniform, but the use of surfactant makes it difficult to clean and often a monolayer persists. Also it is not desirable to use such hazardous surfactant molecules as most of them are not very environment friendly. Therefore we propose a surfactant-less wet-chemical route which combine the advantages of both the methods. Surfactant-less synthesis is already known for 2D Au structures in the form of Au triangles and hexagons but their sizes are in microns. Here we demonstrate the use of support to control particle size of Au to few nanometers by rapid microwave method. CdS-Au has been chosen as the model system to demonstrate the principle in detail. The modification of surface states of CdS-Au hybrid has been discussed along with its effect on optical properties with loading.

    8:00 PM - CC3.24

    Thermodynamic Stability of ZnTe/ZnSe and ZnSe/ZnTe Core/Shell Quantum Dots

    Ying  Qi1, Ryan  Reeves1, Jun  Wang1, T.  J  Mountziaris1.

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    The thermodynamic stability of ZnTe/ZnSe and ZnSe/ZnTe core/shell quantum dots (QDs) was studied experimentally by monitoring the evolution of their near-surface elemental composition using X-ray photoelectron spectroscopy (XPS). Core/shell QDs were synthesized using established protocols involving injection of precursors into a hot mixture of coordinating solvents consisting of hexadecylamine (HDA) and trioctylphosphine (TOP). The precursors used in this study were diethylzinc, selenium powder dispersed in TOP, and tellurium powder dispersed in TOP. QD cores with average size of 2.3 nm were grown and capped with thin shells. Transmission electron microscopy (TEM) was used to measure the core size and shell thickness. Samples were extracted during shell growth, performed at 235 degrees Celsius, and the near-surface elemental composition of the QDs was measured using XPS. For ZnSe/ZnTe core/shell QDs, the near-surface elemental composition rapidly evolved during shell growth and reached a plateau corresponding to a Te-rich surface after 10 minutes of processing. For ZnTe/ZnSe core/shell QDs, the near-surface elemental composition of the QDs evolved more slowly and did not become Se-rich even after one hour of processing. Thermal annealing studies of core/shell QDs were also performed. QDs with 2.3 nm cores and 0.2 nm thick shells were purified and injected into a fresh mixture of HDA and TOP that was kept at 235 degrees Celsius. Samples were extracted at specific time intervals over a period of one hour and the near-surface elemental composition of the QDs was measured using XPS. In both types of QDs, Te segregation towards the surface was observed. The surface segregation of Te was much more pronounced in ZnTe/ZnSe core/shell QDs in comparison to ZnSe/ZnTe ones, indicating higher stability of the latter. The experimental observations are consistent with theoretical predictions of Te surface segregation in ZnSe(1-x)Te(x) ternary QDs [S. C. Pandey et al., Appl. Phys. Lett., 2010, v. 96, 201910].

    8:00 PM - CC3.25

    Photophysical Behavior of Ensembles of Single Semiconductor Quantum Dots

    Kira  D  Patty1, Seyed  Sadeghi2.

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    It is known that the source of photo-enhancement for single quantum dots (SQDs) is surface passivation by photo-induced charge carriers and the formation of additional quantum states in the quantum dots when the core is neutral and the shell charged. This effect has been studied through observation of the blinking behavior over long time scales for colloidal single quantum dots (SQDs) at low excitation intensities. This research explores the blinking behavior of ensembles of single quantum dots over time scales much greater than the blinking of the individual SQDs and how blinking and photo-enhancement are influenced by photo-oxidation. A laser source focused through a high numerical aperture (NA) microscope objective is used to excite an ensemble of SQDs and collect the emissions. Samples are generated to provide a typical separation distance between the quantum dots such that the emissions from SQDs are resolvable (approximately 0.7 microns). The emissions are photographed and analyzed to determine the impact of excitation source intensity on the photoluminescent blinking behavior of both single SQDs and their ensemble. Analysis of the emission photographs shows the presence of large time scale individual and ensemble blinking behavior. At low excitation intensity, photo-enhancement dominates and the total intensity of the ensemble shows a net increase while the emission intensity of the ensemble members/SQDs fluctuates. At high excitation intensity, photo-oxidation dominates and the total intensity of the ensemble shows a net decrease. The emission intensity fluctuations of ensemble members are also observed during photo-oxidation. The fluctuations observed in the total emission intensity are additionally studied using off-resonant and resonant photoluminescence spectroscopy; corroborating the behavior of the ensemble over large time scales.

    8:00 PM - CC3.27

    Suppression of Non-radiative Auger Recombination in Nanostructures with Graded Confining Potentials

    Roman  Vaxenburg1, Efrat  Lifshitz1, Alexander  Efros2.

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    Quantum-confined semiconductor nanostructures have size-dependent optical properties that opened up possibilities for revolutionary advances in semiconductor-based devices, such as light-emitting diodes, lasers, and solar cells. However, application of the nanostructures to real-world devices has been strongly curtailed by the enhancement of dissipative Auger processes that undergird all aspects of carrier relaxation and recombination. Fortunately, according to recent experiments, nanostructures with graded confining potentials may present a route to substantially suppress the rates of the Auger processes [1]. Here we provide a reliable theoretical description of the Auger processes in nanostructures with graded (as opposed to abrupt) confining potentials. We investigate the Auger recombination processes in III-V alloyed heterostructures with gradually varying composition, where the range of carrier densities chosen is similar to the typical operating densities in quantum well lasers and light emitting diodes. The calculations are performed in the framework of the eight-band effective mass approach, accounting for the realistic electronic structure and capturing the major properties of the materials in question. The present study is a generalization of the previous endeavor by G. Cragg and Al. L. Efros [2], where a simplified one-dimensional case was studied. Thus, a fully three-dimensional model has been developed, based on an analytical solution of the effective Schrodinger equation, describing III-V semiconductor heterostructures. The calculations demonstrate that significant quenching of the non-radiative Auger recombination could be reached by varying the degree of smoothness, shape, depth, and width of the confining potential. [1] X. Wang, X., et al, Nature 459, 686 (2009). [2] G. Cragg and Al. L. Efros, Nano Lett.10, 313 (2010)

    8:00 PM - CC3.28

    Fine Structure of the Band Edge Excitons and Trions in CdSe/CdS Core/Shell Nanocrystals

    Andrew  Shabaev1, Anna  Rodina2, Alexander  Efros3.

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    Size-tunable optical properties of colloidal nanocrystals (NCs) makes them promising for a variety of applications. Growing attention to CdSe/CdS core/thick shell NCs (“giant NCs”) is stimulated by their superior optical properties over any other NC heterostructures prepared up to now. The photoluminescence is never completely quenched in these NCs and the blinking is almost completely suppressed. At low temperatures these structures demonstrate suppression of non-radiative Auger recombination and almost 100% photoluminescence quantum yield. These outstanding optical properties are associated with a suppression of the nonradiative Auger recombination of charged excitons and biexcitons. To understand the unusual and potentially useful properties of the giant NCs we have conducted theoretical analyses of the fine structure of the band edge excitons, trions and biexcitons. The theory takes into account the multiband structure of the valence band, complex structure of the inter-particle Coulomb interaction as well as temperature dependence of the conduction band offset, which transfers the quasi-type II CdSe/CdS structure into type I at low temperatures. The calculations allow us to explain temperature dependence of the radiative decay time and the suppression of the nonradiative Auger recombination observed in the giant CdSe/CdS core shell NCs.

    8:00 PM - CC3.29

    Enhanced Photoluminescence and White LED Application of Self-assembled and Encapsulated QDs in the Silica Nanospheres

    Kyoungja  Woo1, Ho Seong  Jang1, Wooyoung  Park1.

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    Functional nanocomposites consisted of quantum dots (QDs) and silica spheres have been widely studied to take advantage of unique optical properties of QDs and high stability and well-known surface chemistry of silica materials. Recently, we have reported the enhanced photoluminescence (PL, 2~3 times of the starting QDs) of QDs self-assembled and encapsulated in the silica submicrospheres, where the order of PL enhancement according to the composite diameter was experimentally 300 nm > 900 nm > 70 nm. However, we reasoned that the PL enhancement of 70 nm sized composite could be improved further, since the light scattering effect could be reduced if we can control the aggregation of nanocomposites. In this study, we have improved the PL enhancement far more (up to ~10 times of the starting QD-MPA) by synthesizing the nanocomposites with reduced degree of aggregation and have shown that the nanocomposite could be integrated for white LED packaging with better color rendering index (CRI). The current nanocomposites are consisted of a silica core (~60 nm) with aminopropyl moieties, a self-assembled QDs layer, and a silica shell. For a typical synthesis, the silica cores were adjusted to pH ~4 for a positive charge. The surface of CdSe/CdS core/shell QDs were modified with mercaptopropionic acid (MPA) and adjusted to pH ~10 for water-solubility and a negative charge. Slow addition of silica cores into QD solution developed self-assembled QDs on the silica core, which were then encapsulated with silica to produce a stable core/shell/shell composite structure with enhance PL intensity. The fabrication of white LEDs using the current nanocomposites (1%), together with blue LED and yellow phosphor (YAG:Ce, 10%), showed efficacy = 61.9 lm/W and CRI = 71.3, which was compared with the case without nanocomposites showing 86.6 lm/W and CRI = 65.4. In summary, we have shown the synthesis of silica nanospheres encapsulating QDs with far more enhanced PL intensity and their integration into white LED packaging with improved CRI. Further collaborative study is under way to reveal the theoretical reason for the enhanced PL intensity.

    8:00 PM - CC3.30

    Aggregation Induced Enhanced Emission in a “Donor-acceptor” Triphenylamine: Effect of Aggregate Size

    Akshay  Kokil1, J.  Matthew  Chudomel2, Boqian  Yang2, Michael  D  Barnes2, Paul  M  Lahti2, Jayant  Kumar1.

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    Organic fluorescent dyes due to their interesting opto-electronic properties have found potential applications in the area of sensing and organic electronics. These dye molecules display high fluorescence quantum yields in dilute solutions, since the interaction between two fluorophores is minimal. However, for concentrated solutions and in solid state the fluorescence is highly quenched. The quenching of fluorescence in aggregated state has been attributed to a variety of non-radiative relaxation pathways the exciton can follow. Recently a class of fluorescent conjugated molecules was reported that displays the opposite effect. In these molecules the quantum yield of fluorescence increased upon aggregation and the effect was named aggregation induced enhanced emission (AIEE). AIEE has been reported in donor - acceptor dyes containing strong electron donating and withdrawing groups. However, the effect of aggregate size on the PL intensity has not received much attention. Here we present detailed photo-physical investigation of the AIEE characteristics of a “donor-acceptor” triphenylamine with weak donor and acceptor moieties. We also correlate the size of the aggregates to the fluorescence properties. We observed that the properties of the surrounding medium can have a significant impact on the AIEE properties. Concomitantly, the size of the formed particles influences the photo-physical properties of the aggregates. We observed that a critical aggregate size is required for obtaining the enhancement in fluorescence. The dependence of the critical aggregate size on the nature of the utilized solvent - non-solvent mixture will also be discussed.

    8:00 PM - CC3.31

    Engineering Optical Interaction of Resonant Semiconductor and Metallic Nanostructures

    Pengyu  Fan1, Mark  L  Brongersma1.

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    It is well known that metallic nanostructures are optical resonators that support plasmonic resonances due to excitation of collective free electron oscillations. In recent years, it is shown that high index semiconductor nanostructures (e.g. Si, Ge nanowires) are also optical resonators that support Mie resonances. In this work, we will discuss strategies of combining optical resonances in metallic and semiconductor nanostructures in hopes of achieving novel optical responses from such hybrid nanostructures due to interactions of optical modes of different nature. We will show examples of structures that combine gold and silicon which exhibit optical cloaking, enhanced optical response and tailored polarization response, all of which can be rationally designed and engineered. We will also demonstrate optoelectronic devices that take advantage of these novel optical response from hybrid semiconductor/metal nanostructures, such as invisible photodetector, highly efficient and compact photodetector, and other potential applications for sensing, imaging and photovoltaics.

    8:00 PM - CC3.34

    Observed Red-shifted PL Emission with Reduced Size in Si Nanocrystals not Due to Intrinsic Γ- Γ Transitions

    Jun-Wei  Luo1, Benjamin G.  Lee1, Paul  Stradins1, Ingrid  E.  Ingrid E. Anderson2, Daniel  Hiller3, Margit  Zacharias3, Alex  Zunger4.

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    Recently, de Boer et al reported a remarkable redshift of excited PL band in Si nanocrystals embedded in a SiO2 matrix as reducing the size. This band starts from about 3 eV at diameter 5.5 nm and reaches at diameter 2.5 nm 1.98 eV. This emission was assigned by the authors to Γ- Γ direct band gap transitions despite the common expectation that quantum confinement should lead to blue shift as size is reduced. De Boer et al using effective mass models by assuming a negative effective mass of Γ-electron supported this assignment. Here we analyze the absorption spectra of Si nanocrystals both via theoretical calculations using state-of-the-art atomistic pseudopotential method and by experimental measurements of two different types of samples. To test the hypothesis of de Boer about the intrinsic (non surface defect) origin of the effect, we have removed in our atomistic simulation surface states by embedding the Si nanocrystals in a widegap matrix, so the results must reflect intrinsic physics. Although surface defect related transitions were frequently observed in photoluminescent (PL) spectrum of Si nanocrystals, in absorption spectrum its relative weak signal shouldn’t mask the strong signal of direct bandgap transitions, which is reflected in the bulk crystalline Si spectrum as a sharp jump. However, in both our atomistic simulation and experimental measurements, no redshift of this sharp jump is observed in absorption spectra as reducing the Si nanocrystal size. To further distinguish real direct Γ- Γ transitions from quasidirect Γ-X transitions in absorption spectra, we perform a projection of our atomistic calculated electron states of Si nanocrystals to bulk Bloch states including Γ, X, and L. We indeed find that as nanocrystal size is reduced the Γ-derived states are blue shifted, which explains why there is no redshift of direct band transitions observed in our Si nanocrystal absorption spectra. Instead, the Γ-X coupling is significantly increased, especially for states close to bulk Γ-electron in energy, upon reducing the size. We conclude that the observed redshift hot PL peak is due to a surface-state radiative channel rather than quantum confinement induced channel. We do clearly observe enhanced light absorption in Si nanocrystals in comparison to in bulk Silicon below the bulk Γ- Γ direct bandgap transitions (3.2 eV). We assign this enhanced absorption to interface induced Γ-X coupling of electron states in Si nanocrystals.

    8:00 PM - CC3.36

    Si Quantum Dot with Giant Absorption Coefficient: 40-fold Greater than Bulk Si Realized by Pulsed Laser Ablation in Liquids

    Takumi  Kitasako1, Ken-ichi  Saitow1 2.

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    A quantum dot (QD) has recently attracted much attention in material science and industrial applications. This is because many distinct optical properties appear by reducing the particle size to an order of nanometer. Namely, the band gap energy, luminescence wavelength, and transition probability are tuned by changing the QD size. In particular, Multi-Exciton Generation (MEG) of QD has been investigated extensively in various QD systems, e.g. PbSe, PbS, PbTe and so on. The reason for the extensive researches on MEG is an excellent property for developing new-generation photovoltaic. Since such a MEG effect has been discovered in silicon (Si) QD, the absorption process of Si-QD has been further crucial topic. Recently, the Si-QDs have been synthesized by various methods, e.g., chemical synthesis, decomposition of silane gas via plasma process, electrochemical etching of Si wafer, and laser ablation. We have fabricated Si-QDs by pulsed laser ablation of Si crystal in liquids. This method has several excellent properties. i) easy process such as 1 step and 1 pot synthesis, ii) QDs are dispersed in solution, iii) QD size of an order of nanometer is easily obtained in a short time, iv) easy surface passivation of QD by solvent molecules. Here we show the Si-QD synthesis by pulsed laser ablation in various organic liquids. The obtained Si-QDs were investigated by dynamic light scattering, UV-Vis-near IR absorption spectrum, FT-IR spectrum, and ICP-OES. As a result, it was ensured that the average size of Si-QDs is 1.1 nm. The absorption coefficient is 10-100 times larger than those of amorphous and crystal Si. Note that the absorption coefficient at the wavelength of 520 nm, in which the maximum of the sun power spectrum exits, is 40 fold greater than that of bulk crystal silicon. In addition, we ensured that the molar extinction coefficient of generated Si-QD at 350 nm is 3 times larger than the published those of all Si-QDs that have the similar size to the current QDs. According to the FT-IR measurements, the surface of Si-QDs passivated by oxygen and carbon atoms was revealed from the observation of Si-C and Si-O vibrational modes. In conclusion, it was considered that very small size (1.1nm) and the surface passivation accomplishes the giant absorption and molar extinction coefficients of current Si-QDs. We will report the solvent dependences of extinction coefficient, size, concentration, spectral shape, and band gap energy of Si-QDs.

    8:00 PM - CC3.37

    Optical and Structural Characterization of Li-doped CdS Nanoparticles

    Ugaliel  Sandoval1, M.  E.  Hernandez Torres2, J.  M.  Gracia Jimenez1, N.  R.  Silva Gonzalez1.

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    It is a well-known fact that the quantum confinement modifies the electronic structure of nanoparticles when their radius is comparable to or smaller than the exciton Bohr radius. On the other hand, the nanoparticles doping leads to phenomena not found in the bulk because their electronic states are confined to a small volume. The most common strategy for doping is to include in the synthesis a precursor containing the impurity. CdS:Li nanoparticles were synthesized using cadmium chloride (CdCl2), thiourea (H2NCSNH2) and lithium chloride (LiCl) dissolved in a stabilizing agent or surfactant (oleylamine). In this case, the nanoparticles growth and the passivity of the dangling bonds are controlled by the surfactant in the solution. The main objective of this work was to study the effect on the optical and structural properties of the CdS nanoparticles produced by the Li incorporation. The study was carried out by means of the optical transmission, photoluminescence, X-ray diffraction and HR-SEM techniques. From transmission measurements the optical energy band gap was estimated and values from 3.6 to 4 eV (Eg=2.42 eV in bulk) were obtained. The values depend upon the nominal lithium percentage in the nanoparticles. The photoluminescence spectra present a line placed at 455 nm (512 nm for the material in bulk). No shift in the peak position was observed in the spectra, which suggests that the electronic levels generated by the doping process are very close to the conduction band. However, a significant change in the peak intensity is exhibit, which varies with the amount of lithium. The X-ray patterns show that there is no displacement of the peaks with respect to their position in bulk material, indicating that no significant changes in their lattice parameters. A particle size of about 5 nm was estimated using the Scherrer equation, which is in agreement with high resolution scanning electron microscopy measurements. This work was partially supported by VIEP (HETM-ING10-I, GRJJ-EXC10-G) and SEP (BUAP-CA-190). The author have a fellowship of CONACYT No 211081.

    8:00 PM - CC3.38

    RGB Color Changing Microstructures Using Magnetic Nanocomposite Microactuators

    Jiyun  Kim1 2, Sung-Eun  Choi1 2, Howon  Lee1 2, Sunghoon  Kwon1 2.

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    Color changing materials to the external stimuli, such as electric, chemical or magnetic signal, have received a great deal of attention for sensors as well as fabric, paint and many other designing materials. Here, we developed a new color changing microstructure capable of being a pixel of color changing surface. This micostructure contains one dimensionally assembled magnetic nanoparticles which play roles of both one dimensional bragg reflector and magnetic axes. The structural color is generated by this bragg scatterer and changed by tilting the microstructure using the magnetic axes. This strategy offers very simple fabrication and operation method for color changing surface with high resolution. The magnetic nanocomposite material for color changing microstructure is based on a combination of photocurable polymer, PEGDA 258 with 10% photoinitiator, and superparamagnetic nanoparticles. The superparamagnetic nanoparticle consists of several single domain magnetites and this core is capped with negatively charged material and silica shell. The nanoparticles are randomly dispersed in resin without the applied external magnetic field. However, when the magnetic field is applied, they aligns along the magnetic field line forming chain-like nanostructures. If the magnetic field line direction is changed, the aligned nanostructures rotate following the changed field line to minimize the magnetic dipole interaction energy of the system. This self-assembling behavior is exploited both to generate the structural color and the rotational property and to drive microstructure to change the color. To fabricate these microstructures, first, the polymer containing nanoparticles is injected on the partially coated glass substrate. By the application of the external magnetic field, the nanoparticles are self-assembled and the entire area shows a specific color by this regular bragg reflector. And, we photopolymerize a microstructure confining the aligned nanoparticle. After the remaining resin is exchanged to the appropriate environment, the colored microstructure is actuated to change the color. The reflected color is changed by tilting the microstructure because the actuation of the microstructure changes the reflected angle of incident light and the angle dependence of the color is fundamental property of the structural color. The resulting microactuator can obtain all red, green and blue colors originally. In the case of red colored microactuator, by the application of the magnetic field, the microactuator bends changing its color from red to green and blue. As the deflection angle increases, the reflected color is blue-shifted. The color spectrum of the microactuator is directly related to the deflection angle, and the deflection angle can be analyzed using a simple analytical model. Acknowledgement: This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MEST) (2011-0030269).

    8:00 PM - CC3.39

    Impact of Hole Injection Layer and Electron Blocking Layer on Carrier Distributions in III-nitride Visible Light-emitting Diodes

    Russell  Dupuis1, Jeomoh  Kim1, Mi-Hee  Ji1, Jae-Hyun  Ryou1, Mahbub  Satter1, Douglas  Yoder1, Alec  Fischer2, Fernando  Ponce2.

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    We report on the behavior of electron and hole transport and resulting distributions of carriers in III-nitride (III-N)-based light-emitting diodes (LEDs) in relation to the effect of hole injection layers and electron blocking layers (EBLs). In order to effectively trace the influence of the transport of carriers and resulting distributions for radiative recombination, we employed a triple-wavelength (TW)-emitting multiple-quantum-well (MQW) active region which has different In content in each InxGa1-xN QW. In addition, Si doping was introduced in selected quantum-well barriers (QWBs) to intentionally control the carrier transport. LED epitaxial structures with various hole-injection layers and with and without EBLs were grown on (0001) sapphire substrates by metalorganic chemical vapor deposition in a Thomas Swan 6×2″ reactor system. The electro-optical properties of TW-LED structures were characterized from both fabricated LEDs and as-grown LED structures. In the case of the LEDs with higher indium mole fraction in p-InxGa1-xN, emission from QW1 becomes stronger. This gradually increased EL intensity of QW1 compared to QW2 and QW3 for the LEDs with increasing indium mole fraction in p-InxGa1-xN layer indicates that more holes can be transported to the lower QW by hole injection layers. The EL spectrum of the TW-LED without an EBL showed the highest emission peak at QW3, one closest to the p-type layer, and gradually decreased in QWs with increasing distance from the p-GaN layer. For the TW-LED with an InAlN EBL, QW2 has the highest emission peak intensity among the three QWs even at low injection current and the emission from QW1 is also much higher than that of the TW-LED without an EBL. To further investigate the carrier transport, we utilized Si doping in a selected QWB. The Si-doped QWB acts as a hole blocking layer so that the hole transport into lower QWs is hindered and correspondingly, most holes are confined at QW3. We will compare electroluminescence characteristics of TW-LEDs employing InAlN and AlGaN EBLs in comparison to one without EBLs and employing various p-InxGa1-xN layer in order to distinguish the carrier transport and distribution in the active region. This different carrier dynamics and related efficiency droop behavior will be further discussed.

    8:00 PM - CC3.40

    Phonon/Quantum Confinement Effect in Nanoparticles as Thermosensors

    Ashish  Kumar  Mishra1, Liping  Huang1.

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    Nanoparticles (NPs) with sizes less than 30 nm have strong size-dependent Raman spectra and photoluminescence (PL) spectra due to the phonon confinement and quantum confinement effect, respectively [1-2]. Both the phonon confinement and the quantum confinement effect provide a convenient way to characterize the size of nanoparticles by simply using Raman and PL spectroscopy. We explored the phonon confinement effect in anatase TiO2 NPs and the quantum confinement effect in ZnO NPs, together with fast grain growth kinetics in these NPs as thermosensor materials. When TiO2 and ZnO NPs are heated up, their size will grow as a function of temperature and time. The temperature- and time-dependent of grain growth is monitored by measuring the size-dependent Raman and PL spectra. This allows us to forensically retain the complete thermal history (temperature and time) of an event that they went through. Our study showed that both temperature and time can be determined simultaneously by using these nano-thermosensors in the range of 400-800C and 0.3-60 s, assuming that the temperature is constant (a step-function approximation to a thermal spike) during a thermal event. These nano-thermosensors can be loaded into the one-dimensional cylindrical pores (5-30 nm) of mesoporous silica particles (SBA-15), to be used in hostile environments. SBA-15 particles serve as the carriers and protectors for the nano-thermosensors encapsulated inside, which record the thermal history through grain growth during the thermal event. By spatially distributing these bare or encapsulated thermosensors, a spatially and temporally non-uniform thermal environment can be determined by a direct read off their Raman/PL spectra at various locations. 1. V. Swamy, A. Kuznetsov, L.S. Dubrovinsky, R.A. Caruso, D.G. Shchukin, and B.C. Muddle, Finite-size and pressure effects on the Raman spectrum nanocrystalline anatse TiO2, Physical Review B, 71, 184302 (2005). 2. K. Lin, H. Cheng, H. Hsu, and W. Hsieh, Band gap engineering and spatial confinement of optical phonon in ZnO quantum dots, Applied Physics Letters 88, 263117 (2006).

    8:00 PM - CC3.41

    Solvent Tunable Polymer Film with a Photonic Structure by Imprinting the Helical Structures on Polymer Matrices

    Chih-Chieh  Chien1, Jui-Hsiang  Liu1.

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    A solvent tunable polymer film synthesized from a bifunctional monomer BAHB, 4,4’-bis(6-(acryloyloxy)-hexyloxy)biphenyl with a photonic structure as a new photonic band gap (PBG) material has been developed by imprinting the helical structures on polymer matrices through multiple photocrosslinking in an induced chiral nematic mesophase. With increasing the times from one time to seven times of photocrosslinking/diffusion procedure, the density of the polymer structure in UV irradiated area was increased due to the diffusion of more amounts of monomers. Here, the polymer matrices themselves served as a chiral template, which exhibited Bragg reflections in the absence of both a chiral dopant and anisotropic materials due to the memory effects of the polymer network. Tuning of colors from blue to red was achieved by making a refractive index contrast in the two periodic media of imprinted solid helical structure and the isotropic liquids that fill it. Upon incorporation of various isotropic liquids, such as methanol, acetone, chloroform, THF and toluene, in the imprinted matrices, a sharp peak in the reflection spectrum shifted drastically from 452 to 658 nm, which indicated that the wavelength shifts strongly depended on the sort of liquids that filled the matrices. The effects of temperature on the imprinted polymer template feeding the various liquids were studied through the reflectance spectra. The fabricated sample cell exhibits a significant reflection band even though the cell temperature is higher than the clearing temperature 118oC. This result suggests that filling the cell with isotropic materials could also reflect the incident light, revealing Bragg reflection. As far as we know, this is the first report regarding the fabrication of solvent tunable photonic films using imprinting methods.

    8:00 PM - CC3.42

    Molecular Orientation and Photoswitching Kinetics on Single-Walled Carbon Nanotubes by Optical Second Harmonic Generation

    Jonathan  Choi1, Changshui  Huang1, David  J.  McGee2, Myungwoong  Kim1, Bastian  Braeuer2, Padma  Gopalan1.

    Show Abstract

    Electronically interfacing light responsive macromolecules or small molecules with multi-walled or single-walled carbon nanotubes (SWNTs) opens up possibilities for new types of photodetectors, light-gated transistors, and energy storage devices. Here, the orientation and photoisomerization kinetics of a monolayer of azobenzene chromophore on SWNTs was probed using optical second harmonic generation (SHG). The monolayer of chromophore was created by non-covalently anchoring a pyrene functionalized Disperse red 1 (DR1P) onto the SWNTs. With a coverage of 3 chromophores per 100 carbon atoms on SWNTs, the p-polarized SHG is sufficiently above the noise to measure the SHG angular dependence for both s and p polarized fundamental, enabling the measurement of an average chromophore tilt angle of 40 ± 3 degrees. Reversible switching between the trans and the cis form was achieved by cycling illumination of a 495 nm LED. Chromophores in the cis state form a dense layer on the nanotube sidewalls, with steric interactions that would be expected to alter the first order cis-trans back-isomerization kinetics commonly observed in solution. The evolution of the SHG signal presented biexponential time constants for 495 nm illumination representing cis-trans back-isomerization kinetics which were T1 = 7.6 s and T2 = 75.3 s. The biexponential kinetics observed here have also been observed for DR1 in a polymer host, in which the cis-isomers were trapped in a strained conformation, leading to an anomalously fast component of the relaxation; in these polymer systems the fast constants were reported to be ≈ 0.3 ~ 0.5 s-1, with the slow constant an order of magnitude larger. As a control, identical illumination experiments with 710 nm light resulted in a very different behavior with no detectable changes in SHG signal since 710 nm is well beyond the λmax of DR1P and illumination at this wavelength should dramatically slow the rate of trans-cis isomerization. Upon applying an electric field, chromophore orientation was significantly enhanced and the cis-trans back isomerization time constants were effectively controlled. The electric field dependence suggests that the gate field of hybrid SWNT-chromophore transistors can act analogous to a poling field, controlling both the chromophore orientation and dynamics. These results are consistent with previous studies of chromophore/SWNT hybrids configured as transistors and provide evidence that trans-cis photoisomerization is responsible for light-induced changes in SWNT-chromophore transistors. Our use of SHG to probe chromophore orientation in hybrid nanotubes should be applicable to a wide range of current research in these systems, including nanotube-hybrids as tunable photodetectors, functionalization of multi-walled nanotubes, and azo-benzene containing polymers wrapped on nanotubes.

    8:00 PM - CC3.43

    Significant Fluorescence-intensity Enhancement by Silicon: Enhancement Effect Studied by a Single Particle Spectroscopy

    Ken-ichi  Saitow1 2, Hidemi  Suemori2, Hironori  Tamamitsu2.

    Show Abstract

    When noble metal nanostructure is optically excited, localized surface plasmon is generated, which produces large electric field at the nanostructure surface. When a molecule near the surface is excited by such large localized electric field, Raman and fluorescence intensities increase dramatically. Thus, various research groups have reported fluorescence-intensity enhancement effect as metal-enhanced fluorescence (MEF). According to recent review articles on MEF, almost researches of MEF have been conducted using gold or silver nanoparticles, and a typical value of fluorescence-intensity enhancement factor (EF) has been 20. On the other hand, large enhancement factors were reported using a bow-tie-shaped gold nanoantenna (EF=1340) and a Au/Ag bimetallic nanostructure (EF=4000). These values are very large as EFs of MEF, but are significantly smaller than EF of surface enhanced Raman scattering (SERS), e.g. SERS EF ranging from million to billion. To realize the high EF for MEF, the crucial issue is how to reduce fluorescence-intensity quenching via energy transfer from excited molecules to the substrate metal. We investigated whether the fluorescence intensity can be enhanced using silicon (Si) particle. Si is a typical semiconductor material and has the following characteristics: (1) It is an indirect-transition semiconductor that can reduce fluorescence-intensity quenching due to forbidden transition. That is, energy transfer from a fluorescent molecule to an enhancement substrate may be suppressed. (2) it is nontoxic and exists in great abundance, and (3) it is inexpensive, because high purity Si is not required for an enhancement substrate. Accordingly, if the enhancement effect is observed with Si, the development of economical enhancement substrates formed of a nontoxic quench-free material would be possible. That is, the number of practical applications will increase, such as those involving high-sensitivity biosensors and LED-intensity enhancement. Here we show the fluorescence intensity of crystal violet (CV) solution using Si fine particles of submicron size. The fluorescence-intensity enhancement was measured under the condition of a single Si particle measurement using fluorescence microscope spectrometer. That is, Si fine particles with the diameter of 500 nm gave the enhancement factor of dye molecules up to 500, whose value is 20 times larger than a typical fluorescence-intensity EF using a noble metal nanoparticle. By measuring the EFs and scattering spectra as functions of particle size, we revealed that the localized electric field at the Si fine particle causes the fluorescence-intensity enhancement of crystal violet.

    8:00 PM - CC3.44

    Photochromic Behavior of Titaniasilicate ETS-10

    Melda  Isler1, Sezin  Galioglu1, Zeynep  Demircioglu3, Rasit  Turan3, Burcu  Akata1 2.

    Show Abstract

    Photochromism is the reversible conversion of a chemical species that describes a change of color in the presence of ultraviolet (UV), visible light. Photochromism is great of interest for some applications, such as rewritable color copy paper, multiwavelength optical memory, holographic data storage and smart glasses [1]. TiO2 is one of the most popular photochromic materials being used due to its adjustable semiconductor property; however it needs to be doped with novel transition metal silver to obtain and enhance this property. Upon exposure to visible light, electrons of silver nanoparticles migrate to the conduction band of TiO2, which activates the oxidation of Ag0 into Ag+ species. This reversible transformation can be observed from the initial brownish-gray color change as a result of its interaction with visible light and the following color change back to the initial starting color with UV light [2]. Accordingly, in the current study, the potential of using Engelhard Titanosilicate (ETS-10) for photochromic applications was investigated that can be of interest due to the distinctive nature of ETS-10, which contains uniquely arranged -Ti-O-Ti-O-Ti- chains that are regarded as a 1-D quantum confined form of titania with a band gap energy of 4.03 eV. For this purpose, Ag+ loaded ETS-10 microcrystals were obtained and their thin films were fabricated successfully. Ag0 nanoparticles were formed on ETS-10 nanocrytals by thermal treatment of ETS-10 at 200, 300, 400, and 500 °C. It was observed that 10-30 nm Ag0 nanoparticles were successfully formed at 500 °C and their distribution on the crytals was very homogeneous. Then, they were subjected to visible light to investigate the reversible transformation into Ag+ in order to achieve the photochromic behaviour. The yellow color of Ag loaded ETS-10 film observed after thermal reduction had disappeared and the films had become semi-transparent with Visible laser exposure. The extent of transformation was investigated as a function of Visible Laser exposure parameters, such as 600 mm/s of rate, 15 kHz of frequency, 20-24 mA of current. The consistent change from Ag0 to Ag+ as a function of the harshness of such parameters was observed by UV-Vis Spectrophotometer, X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), and Scanning Electron Microscopy (SEM) measurements. Accordingly, the photochromic behavior observed for the first time can be ascribed to the -Ti-O-Ti-O-Ti- quantum wire. References: [1] Crespo-Monteriro, N., Destouches, N., Nadar, L., Reynaud, S., Vocanson, F., Michalon, J.Y., Irradiance Influence on the multicolor photochromism of mesoporous TiO2 films loaded with silvernanoparticles, Applied Physics Letters, 99, 173106, 2011 [2] Naoi, K., Ohko, Y., Tatsuma, T., TiO2 films loaded with silver nanoparticles: Control of Multicolor Photochromiic Behavior, Journal of Chemical Society, 2004, 126, 3664-3668

    8:00 PM - CC3.45

    Polarized Light Emission from InGaN Light Emitting Diodes by Utilizing Subwavelength Metallic Grating Structure

    Liyuan  Deng1, Jinghua  Teng2, Chan Choy  Chum2, Soo Jin  Chua1 2.

    Show Abstract

    Considerable research in the past decade on improving output power and reducing cost of GaN-based light emitting diodes (LEDs) has led to their successful commercialization in areas such as solid-state lighting, large-panel display and back lighting for liquid crystal displays (LCD), with the advantages of high brightness, low power consumption and long lifetime. On the other hand, specialized LEDs such as LEDs with polarized light emission are also highly desirable for their potentials to make the imaging and display systems more compact and robust. In this work, we demonstrate a novel way of producing polarized light emission directly from InGaN/GaN multiple quantum well (MQW) LEDs by integrating subwavelength metallic gratings with the LED chip. Subwavelength aluminium gratings are fabricated on top of the p-contact layer of InGaN LEDs grown on sapphire substrate by metalorganic chemical vapour deposition (MOCVD). To explore the grating period dependent polarization performances, gratings with different periods ranging from 150 nm to 300 nm in step of 50 nm are fabricated. Both blue (center wavelength 450 nm) and green (center wavelength 520 nm) LED chips are used for comparison. It is shown that the smaller period grating renders better polarization performance and the subwavelength gratings are more effective for longer wavelength lights. Two-dimensional finite-difference time-domain (FDTD) analysis is performed to fully examine the polarization behavior of subwavelength metallic gratings. The trends predicted by simulation agree well with the experimental data.

    8:00 PM - CC3.46

    Solution-derived NiSi Nanostructure Cermet for High Temperature, High Performance Solar Selective Absorbers

    Xiaoxin  Wang1, Xiaobai  Yu1, Haofeng  Li1, Jifeng  Liu1.

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    Solar selective absorbers, which maximize solar absorption and minimize thermal emittance losses, are important components for concentrated solar power (CSP) systems in converting optical power into thermal energy. The development of solar selective absorbers operating at high temperatures >500 C is of particular interest since high temperature operation offers higher steam turbine efficiency. The main requirements for high-temperature solar selective absorbers are high solar absorptance, low thermal emittance in the mid-infrared regime, and good thermal stability at temperatures >500 C. In our previous work, we demonstrated solution-derived Ni nanochain-Al2O3 cermet with >90% solar absorptance, <10% thermal emittance, and thermal stability up to 400 C. This performance is comparable to conventional cermets fabricated by more costly vacuum deposition technology. It is also found that the metal nanostructures have enhanced solar absorption efficiency due to the surface plasma polariton (SPP) mechanism. In this work, we extend our investigations to a new NiSi nanostructure-SiO2 cermet solar selective absorber with thermal stability up to 700C. NiSi exhibits metallic behavior in electrical and optical properties, while its thermal stability and resistance to oxidation are far superior to metal materials. Due to this reason, it has been widely used in integrated circuits for high thermal stability, low resistivity electrical contacts. However, NiSi-based high-temperature solar selective absorbers have never been investigated in literature. Our optical simulations show that the absorption cross-section of plasmonic NiSi nanostructures is 3~4 times larger than Ni nanostructures of the same feature size in ultraviolet and visible regime, and 7~10 times larger in the near-infrared regime of the solar spectrum. NiSi nanostructures embedded in SiO2 matrix are fabricated by spin-coating a suspension of Ni nanochains dispersed in hydrogen silsesquioxane (HSQ) solution, followed by annealing in N2/H2 forming gas. Upon annealing, HSQ undergoes phase separation into Si nanoclusters embedded in SiO2, which then react with Ni nanochains to form NiSi nanostructures. X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to characterize the nanostructured NiSi formation process and optimize the NiSi fabrication parameters. To increase the load of NiSi nanostructures in SiO2 matrix, we also investigate the spin-coating and reaction process of HSQ/Ni nanochain multilayers with different layer thicknesses. The solar absorptance and thermal emittance are evaluated using ultraviolet-visible-near infrared spectroscopy and Fourier transform infrared spectroscopy (FTIR), respectively. The preliminary results indicate that the solution-derived NiSi nanostructure-SiO2 cermet is a promising candidate for high-performance, low-cost, and thermally stable solar selective absorbers up to 700C.

    8:00 PM - CC3.47

    Microfluidic Synthesis of Magneto-responsive Colloidal Photonic Crystals with Multiple Photonic Bandgaps

    Jae Young  Sim1, Jae-Hoon  Choi1, Seung-Man  Yang1.

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    Colloidal photonic crystals, the periodic structures of monodisperse colloids, have attracted great attention due to their selective light reflection properties and potential applications. Recently, many researchers have tried to fabricate responsive colloidal photonic crystals to tune the optical properties via external field. For example, magnetic or electric anisotropy was added to the colloidal photonic crystals by using iron oxide or carbon black particles. Due to the net magnetic or dipole moment, structural colors from photonic crystals could be controlled under external magnetic or electric field. However, colloidal photonic crystals in previous researches have limits to the tunable range of photonic bandgaps, which could only display the on-off control of single bandgaps or the limited change of double photonic bandgaps. In this study, we reported microfluidic synthesis of colloidal photonic crystals including multiple and magnetically tunable photonic bandgaps by using different sizes of colloidal nanoparticles and magnetic particles. Cylindrical microfluidic chip with four inlets were prepared by bonding two hemicylindrical channels with two inlets, respectively. The hemicylindrical microfluidic channels were fabricated by conventional photolithography and soft lithographic procedures with poly(dimethylsiloxane) (PDMS). Due to the small Reynolds numbers inside microfluidic channels, four laminar flows could be formed by inserting different fluids through four different inlets. When introducing photocurable solution composed of ethoxylated trimethylolpropane triacrylate (ETPTA) with 5 wt% photoinitiator, cylindrical microparticles, each with four compartments, could be fabricated by photo-polymerization under UV light. We also could synthesize colloidal photonic crystals with multiple photonic bandgaps using photocurable silica suspension including different sizes of silica nanoparticles. Each quarter of cylindrical photonic crystals display diverse structural colors, which could be tuned by adding iron oxide nanoparticles to the photocurable silica suspension and exposing UV light under the magnetic field. Due to the net magnetic moment from aligned magnetic particles, microparticles could be rotated under the external magnetic field. Consequently, multiple photonic bandgaps could be manipulated by application of external magnetic field.

    8:00 PM - CC3.48

    Application of Crossed Structure of TiO2 Waveguides and Microfluidic Channels to Fluorescence Detection System

    Masayuki  Furuhashi1, Takahito  Ohshiro1, Masateru  Taniguchi1, Tomoji  Kawai1 2.

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    Marking of biomolecules by fluorophores is one of the indispensable techniques for investigation of biological activities and identification of biomolecules. Fluorescence microscopes are generally used for the observation. Combination of optical waveguides and microfluidic channels develops optical devices for the fluorescence detection on chips. The downsizing of the detection devices decreases sample consumption, footprint and cost. The key points of the integration are fluorescence collection efficiency of the waveguides and geometric arrangement between the waveguides and the microfluidic channels. In the present study, we develop microfabricated optical devices on Si chips that microfluidic channels cross TiO2 waveguides, and investigate transmission properties of light at the microfluidic channel. In addition, we demonstrate detection of fluorescence from quantum dots in the fluidic channels. The devices were fabricated on Si substrates using microfabrication processes. First, we prepared TiO2 cores of channel waveguides. We formed Cr etching masks on TiO2 film (600 nm) deposited on oxidized Si(100) wafers using photolithography and lift-off process. We obtained linear TiO2 cores by dry etching for the TiO2 layers using CF4/Ar gas mixture. Next, we deposited SiO2 claddings by chemical vapor deposition with Tetraethyl orthosilicate. After making Cr etching masks on the claddings by electron beam lithography, we formed microfluidic channels perpendicular to the waveguides by dry etching. The devices were sealed by Polydimethylsiloxane in order to flow quantum dot solution in the microfluidic channel. Incidence of laser into the waveguides was carried out using a single-mode optical fiber. Transmitted laser was emitted from the edges of the waveguides and was collected by a multi-mode optical fiber. We used a diode-type photodetector for measurement of the photointensities. In the case of measuring of fluorescence, the emitted laser was operated by optical filters. Prior to the detection of fluorescence, we have investigated the variation of photointensity of propagating laser at the microfluidic channels in the waveguides. The photointensities of the transmitted laser decrease as the width of the microfluidic channels becomes wider. The amount of decrease is within the estimation by a classical etalon model. We have found that the drop of photointensities at the fluidic channel of 1 μm width is small, which means that the laser at the channels have enough intensities to excite fluorophores and that emitted fluorescence are efficiently collected by the waveguides. Comparing the kinds of liquid fulfilling the microfluidic channels, we have discovered the photointensity difference of the filtered lights between 8 nM quantum dot solution and pure water. We conclude that the device can detect several hundred of quantum dots, which is estimated by the number of quantum dots in the detection volume.

    8:00 PM - CC3.49

    Enhanced Extraction Efficiency of Y3Al5O12:Ce3+ Ceramic Plate Phosphor with a TiO2 Nanostructure

    Hoo Keun  Park1, Seong Woong  Yoon1, Sung Pyo  Hong1, Young Rag  Do1.

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    A conventional white phosphor-converted light-emitting diode (pc-LED) is composed of a blue LED chip and a yellow [Y3Al5O12:Ce3+ (YAG:Ce)] powder phosphor packed with epoxy resin to obtain white emission. However, this white pc-LED has limited conversion efficiency by high scattering and reflection loss of the emission from the powder phosphor layer. To reduce this loss, a transparent polycrystalline YAG:Ce ceramic plate phosphor (CPP) has been studied. However, the low light extraction efficiency of the CPP by the total internal reflection (TIR) and waveguide effect is the most significant drawback for application in white LED. Therefore, in order to enhance a low extraction efficiency of YAG:Ce CPP, a TiO2 nanostructure as photonic crystal layer (PCL) were coated on YAG:Ce CPP by a combination of polystyrene (PS) nanosphere lithography (NSL), atomic layer deposition (ALD) and reactive ion etching (RIE) processes. First, the PS monolayers with various diameters (350, 580, 960nm) were scooped by the YAG:Ce CPP using a scooping transfer technique based on a water-air self-assembly process. Subsequently, a TiO2 film layer was coated over the PS-assisted YAG:Ce CPP by ALD process. To obtain the TiO2 nanostructure, the TiO2 layer-coated YAG:Ce CPP with PS spheres was etched by RIE process. Finally, the etched YAG:Ce CPP was annealed at 450 °C. The effects of the TiO2 nanostructures with various lattice constants (350, 580, 960nm) were investigated on the extraction efficiency of YAG:Ce CPP. The structural, morphological and optical properties of 2D TiO2 nanostructure PCL-assisted YAG:Ce CPPs on top of a blue LED cup were investigated by performing scanning electron microscopy (SEM), atomic force microscopy (AFM) and photoluminescence (PL) measurements.

    8:00 PM - CC3.50

    Wafer-scale AgIn5S8/ZnS-alloyed NCs-polymer Composite Free-standing Films by Spray Coating Process and Their Application for White LEDs

    Sung Pyo  Hong1, Hoo Keun  Park1, Young Rag  Do1.

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    Yellow light-emitting AgIn5S8/ZnS-alloyed nanocrystals (NCs) were prepared via a facile hot injection method. AgIn5S8 cores were synthesized by injection of sulfur source into a mixture of silver and indium precursors in the presence of 1-dodecanethiol. The photoluminescence (PL) quantum yield (QY) of AgIn5S8 NCs was significantly enhanced via solid-solution with ZnS and their PL emission was shifted toward shorter wavelengths (~30nm). The wafer-scale AgIn5S8/ZnS-alloyed NCs-polymer composite films were fabricated by spray coating process. Because spray coating process is simple and scalable method, this process is apt to fabricate the wafer-scale luminescent films. To fabricate the free-standing films, the AgIn5S8/ZnS NCs-polymer composite films were deposited onto sacrificial ionic substrates (NaCl substrates). The obtained luminescent films were used as a color-converting material in white light-emitting diodes (LEDs). The luminous efficacy, color rendering index (CRI) and correlated-color temperature (CCT) of AgIn5S8/ZnS NCs-based LEDs were measured as a function of the applied current. The development of wafer-scale AgIn5S8/ZnS-alloyed NCs-polymer composite free-standing films by spry coating process in this study provides the many potential applications in the fields of photovoltaic cells, light-emitting diodes and flexible devices.

    8:00 PM - CC3.52

    The Talbot Effect beyond the Paraxial Limit at Optical Frequencies

    Yi  Hua1, Jae  Yong  Suh2, Wei  Zhou1, Mark  Huntington1, Teri  Odom1 2.

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    The Talbot effect is a self-imaging effect of periodic structures under coherent illumination with applications in lithography, interferometry, optical trapping, and array illumination. The Talbot effect, however, is only valid in the paraxial limit where the periodicity, a0, is significantly larger than the illumination wavelength λ. To understand the Talbot effect beyond the paraxial limit, we investigated the imaging property of a periodic Au hole array film with a0 comparable to λ both theoretically and experimentally. We found, depending on the ratio of a0/ λ, the self-images of the hole array were not necessarily periodic in the direction perpendicular to the film, and the self-image distances deviated from the paraxial Talbot distances. These differences from the classical Talbot effect can be explained by the deviation from the phase matching conditions beyond the paraxial limit. Interestingly, defects within the hole array film or above the film were healed in the self-images as the light propagated from the surface. The healing effect can be potentially applied to nano-lithography and imaging where defect-free patterns can be generated from a defective mask.

    8:00 PM - CC3.53

    Nanostructured Cr2+:ZnSe-based Thin Films for Mid-IR Laser Sources

    Patrick  J.  Marino1, Tetyana  Konak1, Zachary  R.  Lindsey1, Vladimir  V.  Fedorov1, Sergey  B.  Mirov1, Renato  P  Camata1.

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    Transition metal doped II-VI semiconductors are promising for tunable middle infrared (mid-IR) laser sources operating in the 2-5 μm spectral range. Cr2+ ions incorporated in ZnSe crystals in particular have allowed room temperature continuous wave (CW) laser operation over a tunable range in excess of 1000 nm in the 2-3 μm region. Lasers based on Cr2+:ZnSe may enable highly specific detection of molecular compounds with unique absorption lines in this spectral region. Mid-IR CW operation of laser sources using bulk crystals of this material has been demonstrated at room temperature with slope efficiency and output power greater than 60% and 10 W, respectively. Lasing in Cr2+:ZnSe waveguiding thin-film structures has also been achieved under optical excitation, although with significantly lower efficiencies. In this work we explore the fabrication of nanostructured multilayered Cr2+:ZnSe-based thin films with potential for lasing under electrical excitation and enhanced efficiency of energy transfer from charge carriers in the II-VI host to the Cr2+ optical centers. Thin films of alternating layers of Cr2+:Zn1-xCdxSe (active layer) and ZnSe are created by pulsed laser deposition (PLD) on ITO-coated quartz substrates. The choice of x = 0.2 in the active layer composition leads to an energy gap of 2.5 eV (compared to Eg = 2.7 eV of ZnSe) enabling confinement of optically and electrically injected carriers in the region of the mid-IR active impurities. Nominal thickness of individual active layers is varied between 1 and 10 nm based on deposition rate calibration. Thickness of the intervening ZnSe layers and total number of alternating layers are kept fixed at 20 nm and 30, respectively, leading to overall thickness of the structure in the 100-1000 nm range. The chosen thicknesses of the active layer should enhance energy transfer from excitons to the Cr2+ ions due to their close proximity in the confined region and the increased oscillator strength of excitonic recombination due to quantum confinement. PLD is carried out using solid ZnSe and Cr-doped Zn0.8Cd0.2Se ceramic targets. Targets are prepared by mixing powder precursors, compressing them into solid pellets and annealing. Cr-doped pellets are annealed in sealed quartz ampoules at 1000°C for 10 days to ensure diffusion of Cr impurities. Targets are ablated by a KrF excimer laser at 2 J/cm2 at pressures below 1 × 10-6 Torr with substrate temperature kept at 550°C. Deposited thin film structures are analyzed by atomic force microscopy (AFM) for surface morphology and by X-ray diffraction (XRD) and Raman spectroscopy to characterize the crystalline quality of the films. The optical absorption and emission characteristics of the multilayered films are used to verify the incorporation of Cr2+ ions into the II-VI host and evaluate the effect of structure characteristics (layer thickness and dopant concentration) in the potential of the nanostructures for lasing operation.

    8:00 PM - CC3.55

    Color Tunable Organic Plasmon-emitting Diodes

    Illhwan  Lee1, Kisoo  Kim1, Sungjun  Kim1, Bon Hyung  Koo1, Bola  Lee1, Jong-Lam  Lee1.

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    A variety of strategies have been adopted for the fabrication of color-tunable OLEDs, including emissive layer doping, use of exterior color tuning layers, and use of interior complex layers. Although these methods can tune the emission color, they have several limitations, such as degradation of electroluminescent properties, complex processing techniques, and high-cost fabrication procedures. In this work, we demonstrate a novel way of emission color tuning of an OLED by embedding Ag nano-dots between the anode and organic materials of the OLED. We observed the increases in the magnitude of absorbance and the emission spectra shift toward longer wavelengths (red shift) according to the increase of Ag nano-dot size and spacing. These results suggest that Ag nano-dots can effectively generate LSPs resonance at the ITO/Ag interface and that their size and spacing determined the emission color of the OLED. Using the LSPs resonance, we demonstrated color-tunable OLEDs of various emission colors from cyan to yellow-green. This report presents a useful and simple fabrication route that is widely applicable to optoelectric devices.

    8:00 PM - CC3.56

    Plasmonic/Electronic Properties of Pt@Ag Core@Shell Nanoparticles

    Anh  Thi Ngoc  Dao1, Prerna  Singh1, Derrick  Mott1, Shinya  Maenosono1.

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    Noble metal nanomaterials with interesting physical and chemical properties are ideal building blocks for engineering and tailoring nanoscale structures for specific technology application, such as analytical sensors or fuel cell catalysts. Among them, Ag nanomaterials are of particular interest because Ag nanostructure with different size and shape show a wide range of colors corresponding to their localized surface plasmon resonance. Most importantly, Ag has been used as excellent surface-enhanced Raman scattering substrates because it exhibits the best SERS effects compared with other metals. Meanwhile, Pt is a well-known catalyst that has high catalytic activity, especially for methanol electro-oxidation and oxygen electro-reduction reactions. By building on the well-known properties of this precious metal, platinum has been combined with numerous other metals, such as Pd, Au, Ag, etc. to increase electro-catalysis and attempt to limit the poisoning of the Pt surface by strongly adsorbed intermediates (e.g CO). Therefore, Pt-Ag system has received much attention from researchers and scientists for not only electro-catalytic activity but also SERS. However, there are still many obstacles in the synthesis of core@shell structures. The galvanic replacement reaction poses a challenge to synthesizing uniform Ag@Pt core@shell structures, while successful formation of Pt@Ag core@shell NPs is hampered by lattice mismatch. This presentation focuses on our recent results in the study of Pt@Ag core@shell NPs with controllable size and shell thickness. In addition, the plasmonic properties and unique electronic structure of this system are intriguing and suggest a tunable nature that can be used in catalytic, SERS and other applications. The results are discussed in terms of UV-Vis, XRD, TEM, HR-TEM, EDS, XPS, and HAADF-STEM.

    Download Session Locator (.pdf)2012-11-27  

    Symposium CC

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    Symposium Organizers

    • Matthew Doty, University of Delaware
    • Srikanth Singamaneni, Washington University
    • Andrey L. Rogach, City University of Hong Kong
    • Mark Brongersma, Stanford University
    • Vladimir V. Tsukruk, Georgia Institute of Technology

      CC4: Plasmonic Devices

      • Chair: Harry Atwater
      • Chair: Nader Engheta
      • Tuesday AM, November 27, 2012
      • Hynes, Level 2, Room 208
       

      8:30 AM - *CC4.01

      Plasmonics beyond Shockley and Queisser: Plasmonic Hot Carrier and Plasmoelectric Mechanisms for Optical Energy Conversion

      Harry  A.  Atwater1.

      Show Abstract

      Today's semiconductor photovoltaic energy converters are dominated by photon absorption and photo-carrier generation of electron-hole pairs across a semiconductor band gap. The 'Shockley-Queisser' limit of photovoltaic efficiency dictates that thermalization of hot carriers limits the energy that can be extracted from photons whose energies are above the band gap energy, whereas photons of less than band gap energy are not absorbed. Is it possible that plasmonic mechanisms could enable us to exceed the Shockley-Queisser limit by recovering the energy lost via either hot carrier relaxation or subgap photon non-absorption? We discuss two approaches to this concept: i) plasmonically-generated hot carrier collection mechanisms and ii) ‘plasmoelectric’ mechanisms for power conversion. Hot carriers created by the decay of plasmons excited in resonant optical nanoantennas can be injected across a Schottky barrier to produce a hot carrier photocurrent. We articulate the design approach for plasmonic hot carrier nanoantennas, and discuss the energy conversion efficiency limits of this approach. The plasmoelectric effect is a mechanism for conversion of optical power into DC electrical power using resonant absorption in plasmonic nanostructures. In this effect, an optically-induced electrochemical potential results from the dependence of optically generated heat on the change the plasmon resonance frequency that occur with changes of electron density. We model an all-metal plasmoelectric structure capable of characteristic conversion efficiency of >10% energy conversion under 1 kW m-2 intensity, single-frequency radiation. We discuss strategies for enhanced efficiency, broadband power conversion, and further applications of plasmoelectric power generation.

      9:00 AM - CC4.02

      Exploiting Plasmon Induced Hot Electrons in Optoelectronic Nanostructures

      David  Conklin1, Sanjini  Nanayakkara2, Tae-Hong  Park3, Joshua  T.  Stecher4, Michael  J.  Therien4, Dawn  A.  Bonnell1.

      Show Abstract

      Interest in plasmon-exciton interactions is increasing owing to potential impact in light harvesting and optical signal manipulation. Recently a new mechanism of plasmon induced current generation was observed in porphyrin-Au nanoparticle hybrid nanostructures.[1] The plasmons associated with the gold nanoparticles enhanced photo conduction by many factors even an order of magnitude. To understand this phenomena we have first developed an approach to the analysis of temperature dependent transport measurements that can lead to an unambiguous determination of mechanism in complex systems. [2] Then the temperature and wavelength dependent transport is examined as a function of nanoparticle size and distribution and molecule optical properties. [3] The Au-porphyrin combination is designed to distinguish potential mechanisms for plasmon induced current. We will show new evidence for a mechanism involving 'hot electron' generation. This has the potential to vastly increase efficiency of energy harvesting devices. [1] Banerjee et al ACS Nano 4 (2010) 1019-1025 [2] Conklin et al NanoLetters 12 (2012) doi 10.1021/nl300400a [3] Conklin et al Advanced Materials 21 (2011) 4712-4718.

      9:15 AM - CC4.03

      Development of Single Photon Nanopillar Detectors via 3D Surface Plasmon Absorption and Enhanced Avalanche Gain

      Pradeep  Nuwan  Senanayake1, Chung  Hong  Hung1, Joshua  N  Shapiro1, Andrew  Lin1, Diana  L.  Huffaker1 2.

      Show Abstract

      We demonstrate 3D surface plasmon photoresponse in nanopillar arrays resulting in enhanced responsivity due to both Surface Plasmon Polariton Bloch Waves (SPP-BWs) and Localized Surface Plasmon Resonances (LSPRs). Angular photoresponse measurements show that SPP-BWs can be spectrally coincident with LSPRs to result in x2 enhancement in responsivity at 1045 nm. Full-wave Finite Difference Time Domain (FDTD) simulations substantiate the coupling of the SPP-BW and LSPR for enhanced absorption and the nature of the LSPR. The LSPR is due to a nanopatch optical antenna formed by the gold cap partially coating the nanopillar and the gold ground plane. Avalanche multiplication is also investigated in core-shell GaAs nanopillar arrays resulting multiplication factors ~20 at -12V. Enhanced electric fields in the nanopillar allows a more deterministic multiplication of carriers and breakdown at lower voltages. 3D control of surface plasmon absorption and enhanced carrier multiplication are essential steps towards the realization of plasmonically enhanced nanopillar single photon detectors.

      9:30 AM - CC4.04

      Plexciton-enabled Photon Recycling in Metal-dielectric-metal OPVs

      Matthew  Evan  Sykes1, Kwang  Hyup  An2 3, Max  Shtein1.

      Show Abstract

      The typically short exciton diffusion length is an important factor in limiting the performance of organic photovoltaic (OPV) devices, and presents a trade-off with the need to maximize light absorption. While the bulk heterojunction architecture is one route to breaking this trade-off, the BHJ approach presents a number of other undesirable shortcomings (e.g. potential long-term morphological instability, the need to simulaneously tune solubility and electronic properties, etc.). Another approach is to maximize light absorption for relatively thin, planar structures. Plasmonic structures potentially allow the optical density of states to be increased inside the active organic layers, thereby increasing absorption, but nearly always with parasitic effects (e.g. dissipation as heat) dominating the improved absorption. Here we study the wavelength-dependent enhancement of photocurrent through surface plasmon-exciton (plexciton) coupling in ultrathin, smooth, metal-dielectric-metal (MDM) OPVs. The use of metallic cavities produces a strong optical confinement of the internal waveguided modes and efficient coupling to molecular dipoles throughout the device. We observe a very high, 60% plasmon-to-photocurrent conversion efficiency and an absorption enhancement of 76% above what is predicted from direct absorption through free space-coupled modes. This absorption enhancement follows the trend of the calculated photon density of states in the waveguide and the radiative recombination rate of the donor material, implying that exciton coupling to waveguided plasmon modes through photon recycling further enhances the absorption in subwavelength-scale MDM OPVs. These structures are potentially compatible with simple encapsulation layers and do not require in-plane nanopatterning or external sensitizer layers.

      9:45 AM - CC4.05

      Resonant Surface Plasmon Interactions with High-gain Semiconducting Polymers for SPASER Devices

      Sarah  Goodman2, Jesse  Kohl1, Deirdre  M  O'Carroll1 2.

      Show Abstract

      A laser is a device primarily consisting of a resonant cavity and a gain material that emits monochromatic, coherent electromagnetic radiation and is thus an invaluable tool in various scientific fields. However, the size of a laser is constrained by the diffraction limit, meaning that the light beam it produces cannot be spatially confined to less than a few hundred nanometers, or half the wavelength of the light being emitted in free space. In the past decade, a deeply sub-wavelength analogue to the laser, using surface plasmons instead of photons, has been proposed that exhibits surface plasmon amplification by stimulated emission of radiation, i.e., the SPASER. These devices consist of a resonant metallic nanoparticle, which can support surface plasmons, that is in intimate contact with a high-gain material. SPASERs could enable ultra-small optical amplifiers, higher-resolution microscopes and densely integrated optical communications to be further developed. In recent years, a few experimental demonstrations of SPASER devices have been realized using dye-doped-silica-coated spherical metal nanoshells and semiconductor nanowire/metal film configurations. However, the development of SPASER devices is still in its infancy and further exploration is required to identify SPASER designs that could achieve low thresholds for surface plasmon amplification by stimulated emission, high spatial coherence and both color purity and tuneability. Here, we propose the use of high-gain conjugated polymer semiconductors as the active materials through which surface plasmons are amplified in SPASER devices. The advantages of these materials are: (1) unlike dye molecules, they do not undergo concentration quenching in the solid-state and so a very high chromophore density can be packed into the near-field of the resonant metal nanoparticle. (2) Conjugated polymer gain media exhibit large gain cross-sections (up to 10-15 cm2 for polyfluorene derivatives). (3) The polymer material is far more stable than small organic laser dye molecules. (4) The oscillator strength and transition dipole orientation of the conjugate polymer gain material can be manipulated by controlling polymer chain orientation. In addition to employing high-gain conjugated polymer materials, the use of anisotropic metal nanoparticles instead of spherical metal nanoparticles is expected to yield stronger (i.e., lower loss) surface plasmon resonances and, hence, lower threshold SPASER operation. We will present our recent work on the fabrication of conjugated-polymer-coated gold nanorods using miniemulsion and grafting techniques, and describe the resonant optical interactions between gold nanorods and the conjugated polymer gain material as a function of excitation pump energy.

      10:00 AM -

      Break

      Show Abstract

      10:30 AM - *CC4.06

      Magnetoactive Metastructures

      Nader  Engheta1, Artur  Davoyan1, Uday  K.  Chettiar1.

      Show Abstract

      In this talk, we will present some of our most recent theoretical results of our work on exploring several novel features of nonreciprocal metamaterials and magnetoactive metamaterials. These metamaterials and metastructures involve scenarios in which magnetoactive materials (materials with time-reversal symmetry breaking due to magnetic field) are combined with plasmonic nanostructures or extreme-parameter metamaterials such as epsilon-near-zero (ENZ) structures. We have been investigating, theoretically and numerically, several topics including: magnetic ENZ metamaterials, nonreciprocal plasmonic circuits and interconnects (such as one-way waveguides), notion of one-way hot spots, plasmonic boosting of magneto-optical response, plasmonic antenna with broken time-reversal symmetry, just to name a few. We will discuss some of novel phenomena stemming from such magnetoactive nonreciprocal metamaterials, and will present physical insights behind our findings.

      11:00 AM - CC4.07

      Ultra-thin Perfect Absorber Using a Tunable Phase Change Material

      Mikhail  A  Kats1, Deepika  Sharma1 2, Jiao  Lin1 3, Patrice  Genevet1, Romain  Blanchard1, Zheng  Yang1, Mumtaz  Qazilbash4 5, Dmitri  Basov4, Shriram  Ramanathan1, Federico  Capasso1.

      Show Abstract

      Perfect absorbers have so far involved relatively complex structures consisting of either wavelength-scale asymmetric Fabry-Perot cavities or plasmonic metamaterials. It is commonly assumed that plasmonic elements are necessary for the creation of perfect absorbers with thicknesses smaller than a quarter of the operating wavelength. In this report, we show that perfect absorption can be achieved with a single lossy dielectric layer of thickness much smaller than the incident wavelength on an opaque substrate by utilizing the nontrivial phase shifts at the interfaces between lossy media. This design is implemented with an ultra-thin (~λ/65) vanadium oxide (VO2) layer on a sapphire substrate, with the VO2 temperature tuned in the vicinity of its insulator-to-metal (IMT) phase transition, leading to 99.75% light absorption at λ = 11.6 µm. The operation wavelength can be tailored by modifying the thickness of the VO2 film. The effect can be explained using the language of critical coupling to a resonator, which is formed by the VO2 layer and the substrate. The absence of lithography in device fabrication, its structural simplicity, and its immunity to small variations in material composition enable various large area applications. Furthermore, the large tuning capabilities (from ~80% to 0.25% in reflectivity) enabled by the large variation of optical properties in the vicinity of the IMT are promising for infrared devices such as thermal emitters, modulators, and bolometers.

      11:15 AM - CC4.08

      Electrically Driven Nano-scale Surface Plasmon Sources with Enhanced Subwavelength-scale Integration and Functionality

      You-Shin  No1, Jae-Hyuck  Choi1, Hong-Gyu  Park1.

      Show Abstract

      In recent years, a variety of nano-optical components have been demonstrated including plasmonic amplifiers, lasers and LEDs. However, due to inefficient injection and coupling of surface plasmons, the integration of plasmonic components at the nanoscale remains a major challenge. In this work, we report an electrically driven nano-scale semiconductor surface plasmon source fabricated one-dimensional nanowires and two-dimensional nanoplates by chemically assisted dry etching of an epitaxially grown and a doped AlGaAs/GaAs semiconductor wafer. The device structures are characterized by a vertically-oriented p-i-n junction with an intrinsic region containing AlGaInP/InGaP multi-quantum wells that define the emission range from 600 - 700 nm. We successfully realized electrically driven semiconductor nanowire and nanopalte LEDs with moderate current injections of few μA. In addition, an optimized subwavelength-scale metallic waveguide design demonstrates efficient delivery of electromagnetic energy with high confinement and long propagation lengths. Electroluminescence spectroscopy measurements and CCD image acquisitions confirm that the electrically driven source can efficiently launch and propagate surface plasmons into the optimally designed subwavelength-scale metallic waveguides. To further enhance optical functionality, we introduced adiabatically tapered metallic structures at the end of the waveguides and observed concentration of light down 50 nm and a significant enhancement of electromagnetic field density at the end of the tapered gap.

      11:30 AM - CC4.09

      Multipolar Second Harmonic Generation from Plasmonic Arrays

      Antonio  Capretti1 2, Gary  F.  Walsh1, Salvatore  Minissale1, Jacob  Trevino3, Carlo  Forestiere1, Giovanni  Miano2, Luca  Dal Negro1 3.

      Show Abstract

      In the last few years, the Second Harmonic Generation (SHG) from planar arrays of metal nanoparticles (NPs) has been investigated for a variety of NPs shapes, sizes, and under different excitation-collection and polarization conditions. However, the role of the planar array geometry on the SHG from metallic NPs is not yet fully understood. Using deterministic aperiodic nanostructures (DANS), we investigate the role of the array geometry on the SHG from planar arrays of Au nano-cylinders for progressively increasing structural complexity. Arrays of nano-cylinders are fabricated by electron beam lithography on silica substrates, their plasmonic response is characterized by dark field scatting, and SHG is produced by excitation with 120fs laser pulses at 780 nm. Through polarization-resolved measurements we demonstrate multipolar generation that is largely tunable by the array geometry. We consider the components of the collected signal that are parallel and orthogonal to the scattering plane, defined by the directions of excitation and collection. We measure the SHG intensities of the two polarization components as a function of the input polarization angle of the pump beam. Quadrupolar SHG behavior is clearly displayed by the orthogonal components in quasi-periodic DANS. On the contrary, the photonic interactions among NPs radically modify the SHG radiated from periodic and more disordered DANS. For these array geometries, the polarization patterns of the orthogonal components are different from a pure quadrupole, and clear high order multipolar SHG emission is observed. These results are important for the development of novel optical elements for nonlinear nanophotonics applications, such as switchers, frequency converters and nonlinear optical sensors on a planar chip.

      11:45 AM - CC4.10

      Spin-selective Directional Coupling of Surface Plasmon-polaritons

      Jiao  Lin1 2, Qian  Wang3, J. P. Balthasar  Mueller1, Guanghui  Yuan3, Xiaocong  Yuan4, Federico  Capasso1.

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      We present a plasmonic coupler that unidirectionally converts circularly polarized incident light of opposite handedness (spin) into counter-propagating surface plasmon-polariton (SPP) modes. In addition to the spin-sorting properties, our design enables the conversion of light of arbitrary linear polarizations into SPPs, in contrast to conventional grating couplers. The concept relies on achiral arrays of polarization sensitive subwavelength plasmonic aperture antennas. Its small unit cell footprint and rectangular symmetry enable straight-forward modification to match a broad range of wavelengths and applications. We experimentally demonstrate switchable, unidirectional launching, polarization insensitive coupling and an improved plasmonic lens. The fabricated structures are based on apertures in a flat gold film that are optimized to operate at 632 nm. The designs are optimized with the aid of finite-difference time-domain (FDTD) simulations and fabricated by focused ion beam (FIB) milling into a gold film. The SPP waves are measured by a near-field scanning optical microscope (NSOM) under back-illumination of the structures by a HeNe laser. The device introduced in this report could be useful when precisely controlled coupling between free space light and propagating SPPs is required. The insensitivity to the polarization of the incident light can be used to overcome some of the coupling limitations frequently encountered in plasmonics. This property also has the potential of fully encoding information contained in both the intensity and polarization of light in SPPs, which could have profound impact on future developments in optical information processing.

      CC5: Epitaxial Nanostructures

      • Chair: Peter Michler
      • Tuesday PM, November 27, 2012
      • Hynes, Level 2, Room 208
       

      1:30 PM - *CC5.01

      Optical Manipulation and Analysis of a Single Semiconductor Dopant Atom in a Scanning Tunneling Microscope

      Paul  Koenraad1.

      Show Abstract

      Recently it has become possible to move past the electrical and optical exploration of an ensemble of dopants and to identify the effects of a solitary dopant as well as to study locally the fundamental properties of a solitary dopant atom in a semiconductor. This allows opening the new field of solotronics (solitary dopant optoelectronics). A Scanning Tunneling Microscope (STM) is an excellent tool to probe and manipulate a single impurity either in the surface layer or just a few mono-layers below the clean semiconductor surface. We have recently shown that a silicon atom in the outermost layer of GaAs has a bi-stable character much alike the well-known DX-center in Al(x)Ga(1-x)As. In the ground state the Si atom is negatively charged and in the excited metastable state the Si impurity is positively charged. These two charge states are related to a modification of the bond configuration of the silicon atom in the GaAs surface layer. By a proper electric switching sequence we can bring the silicon atom in either of the two states while probing it with an STM tip. We have successfully used these procedures to create a memory element that is based on a single impurity atom. Next to this electrical manipulation of single impurity atoms, our setup allows to illuminate the tunneling area or to collect tunneling induced photons from the area below the STM tip. We will show our recent results in detecting local STM induced luminescence on doped GaAs crystals. The same setup was used to explore Au surfaces where we are able to observe atomically resolved plasmon excitation. In the study of the bi-stable silicon impurity we have investigated the optically manipulation of the bond configuration and corresponding charge state of a single silicon impurity atom as a function of the excitation wavelength. This allowed us to unravel different pathways for the excitation and relaxation processes that are involved in this manipulation process. In conclusion we show that the electrical and optical characterization and manipulation of a single impurity in a (spin-polarized) STM setup is possible.

      2:00 PM - CC5.02

      Upconversion Spectroscopy of Erbium in Amorphous Aluminum Microstructures

      Laura  Agazzi1, Kerstin  Worhoff1, Markus  Pollnau1.

      Show Abstract

      The influence of energy migration and energy-transfer upconversion (ETU) among neighboring erbium ions on luminescence decay and steady-state population densities in amorphous aluminum oxide microstructures is investigated by means of photoluminescence decay measurements under quasi-CW excitation. The experimental results are analyzed by several models. As expected from the basic physical assumptions made by these models, only Zubenko’s microscopic model provides good agreement with the experimental data, while other donor-acceptor treatments found in the literature are unsuccessful and the macroscopic rate-equation approach provides meaningful results only when misinterpreting the intrinsic lifetime as a free fit parameter. Furthermore, a fast quenching process induced by, e.g., active ion pairs and clusters, undesired impurities, or host material defects such as voids, that is not revealed by any particular signature in the luminescence decay curves because of negligible emission by the quenched ions under quasi-CW excitation, is verified by pump-absorption experiments. This quenching process strongly affects device performance as an amplifier. Since Zubenko’s microscopic model treats all ions equally, it is unable to describe a second, spectroscopically distinct class of ions involving a fast quenching process. The model is extended to take into account the fraction of quenched ions. This approach finally leads to excellent agreement between the luminescence-decay, pump-absorption, and gain experiments within the frame of a single theoretical description [1]. Via luminescence decay measurements, absorption and emission spectra, and a Judd-Ofelt analysis we determine luminescence lifetimes, radiative and non-radiative decay-rate constants, and branching ratios of the erbium inter-manifold transitions. With a continuous-wave pump-probe technique the excited-state absorption (ESA) spectrum is recorded between 900 and 1800 nm and the cross-sections of ESA transitions from the first and second excited state are determined. The microparameters and efficiencies of resonant and phonon-assisted energy-migration and ETU processes among erbium ions occurring from the first and second excited states are evaluated. From the ratio of the green and red luminescence intensities as a function of erbium concentration we prove the existence and quantify the macroscopic ETU coefficient of an additional two-phonon-assisted ETU process [2]. 1. L. Agazzi, K. Wörhoff, M. Pollnau, "Energy-transfer-upconversion models, their applicability and breakdown in the presence of spectroscopically distinct ion classes: Investigations on the example of amorphous Al2O3:Er3+", submitted. 2. L. Agazzi, K. Wörhoff, A. Kahn, M. Fechner, G. Huber, M. Pollnau, "Spectroscopy of upper energy levels in an Er3+-doped oxide", submitted.

      2:15 PM - CC5.03

      Polarization-induced pn-diodes in III-nitride Nanowires with Ultraviolet Electroluminescence

      Santino  D.  Carnevale1, Thomas  F.  Kent1, Patrick  J.  Phillips2, Michael  J.  Mills1, Siddharth  Rajan3 1, Roberto  C.  Myers1 3.

      Show Abstract

      Many solid-state electronic devices utilize a pn-junction, traditionally formed by random doping of donor and acceptor impurity atoms. Here we present a new type of pn-junction not formed by impurity-doping, but rather by polarization-induced p and n conducting regions within compositionally graded non-centrosymmetric semiconductor nanowires.* Linearly grading AlGaN nanowires from GaN to AlN forms the polarization-induced n-type region, while grading back from AlN to GaN forms the p-type region. A quantum disk at the center of the junction serves as the active region for a light emitting diode. Since electrons and holes are injected from AlN barriers into quantum disk active regions, graded nanowires allow deep ultraviolet light emitting diodes across the AlGaN band gap range. While previous work in graded III-nitride planar structures showed that polarization-induced p-type doping was only possible with supplemental acceptor doping, the graded nanowires in this study show that p-type material is possible without the use of supplemental doping. This demonstrates an advantage for polarization engineering in nanowires compared with planar films. Polarization-doping in nanowires provides a strategy for improving conductivity in wide band gap semiconductors. As an added benefit, because polarization charge is uniform within each unit cell, polarization-induced conductivity without the use of impurity-doping provides a solution to the problem of conductivity uniformity in nanowires and nanoelectronics, and opens a new field of polarization engineering in nanostructures that may be applied to other polar semiconductors. The nanowire devices presented here are grown on n-Si(111) substrates by plasma-assisted molecular beam epitaxy. Scanning transmission electron microscopy images and energy dispersive x-ray spectroscopy show that each nanowire is linearly graded from GaN to AlN and back to GaN, as designed. Electroluminescence and current-voltage characteristics are provided for a variety of devices, showing tunable emission from 360 nm (3.44 eV) to 266 nm (4.66 eV). A minimal change in device performance at cryogenic temperatures shows that carriers are not thermally-ionized, but are rather field-ionized by bound polarization charge. A comparison of samples with and without the use of impurity doping is provided to show the effectiveness of polarization-induced doping in III-nitride nanowires. This work is supported by the Office of Naval Research (N00014-09-1-1153) and by the National Science Foundation CAREER award (DMR-1055164). S.D. Carnevale acknowledges support from the National Science Foundation Graduate Research Fellowship Program (2011101708). * S.D. Carnevale, T.F. Kent, P.J. Phillips, M.J. Mills, S. Rajan, R.C. Myers. Nano Lett. 12, 2, 915-920, 2012.

      2:30 PM - CC5.04

      Epitaxial Growth and Ferromagnetism of GdN-III-nitride Nanocomposites and Their Potential Device Applications

      Thomas  Kent1, Jing  Yang1, Limei  Yang1, Santino  C.  Carnevale1, Michael  Mills1, Roberto  Myers1 2.

      Show Abstract

      The epitaxial integration of rare earth pnictides (RE-Pn), such as ErAs and ErSb, in III-As semiconductors has attracted attention for applications in novel high speed photodetectors and photoconductive switches as well as enhanced tunnel junctions. Here we report on integration of the RE-Pn GdN as discrete particles in a GaN matrix by plasma assisted molecular beam epitaxy. It is hypothesized that the growth of GdN particles proceeds in a similar fashion to that of RE-Pn in III-As zincblende systems, with growth proceeding by nucleation of RE-Pn islands followed by epitaxial lateral overgrowth of the surrounding uncovered III-V matrix. Periodic structures of GdN nano-island layers spaced between GaN regions were prepared and subsequently characterized by a variety of methods. High resolution X-ray diffractometery shows that the cubic, rocksalt structure, GdN islands are epitaxially oriented to the hexagonal wurtzite GaN matrix with the relationship GdN [111]||GaN[0001]. The XRD result also indicates the precise layer thickness control due to the presence of superlattice interference fringes. Cross-sectional scanning transmission electron microscopy (STEM) combined with in-situ reflection high-energy electron diffraction (RHEED) allows for the study of island formation dynamics, which occurs after 1.2 monolayers of GdN coverage. Superconducting quantum interference device (SQUID) magnetometry reveals multiple ferromagnetic phases, with one attributable to the GdN particles with Curie temperature of 70K and an anomalous phase with ferromagnetism persistent to room temperature as well as a paramagnetic background, which is proposed to be due to contamination of the GaN matrix with Gd during growth. The room temperature ferromagnetic phase is strongly anisotropic, with out of plane magnetization nearly 300% larger than in-plane at fields less than 1T. In addition, electroluminescent devices were fabricated by embedding GdN nanoparticles in an aluminum nitride matrix. At low device biases of 15V, clear, narrow emission at 318nm is observed, corresponding to impact excitation of Gd^3+ intra-f-shell atomic transitions.

      2:45 PM -

      Break

      Show Abstract

      3:15 PM - *CC5.05

      Self-Assembly of Optically Active Quantum Nanostructures

      Zhiming  Wang1.

      Show Abstract

      From ensembles of quantum nanostructures to their individuals, the self-assembly approach has its advantage on keeping their optically active functionality. In this talk, I’m going to review recent developments not only from the traditional strain-driven self-assembly but also from the droplet epitaxy and their hybrid approach, to cover a rich spectrum of nanostructured morphologies such as quantum rings, quantum-dot molecules, and nanoholes.

      3:45 PM - CC5.06

      Narrow Optical Line Width from Site-controlled InGaAs Quantum Dots

      Lily  Yang1, Michael  K  Yakes2, Timothy  M.  Sweeney1, Sam  Carter2, Mijin  Kim3, Chulsoo  Kim2, Allan  S  Bracker2, Dan  Gammon2.

      Show Abstract

      The incorporation of self-assembled quantum dots in systematically scalable quantum devices requires a method of nucleating dots with nanometer-scale spatial accuracy while preserving their narrow optical line width. We have developed a technique combining e-beam lithography, wet etching, and molecular beam epitaxial (MBE) growth to deterministically position InGaAs quantum dots with spectrometer limited photoluminescence line widths. Previous demonstration of deterministic alignment between self-assembled quantum dots and subsequently fabricated devices employed a two-step process of first locating a randomly positioned dot, then fabricating a device around it [1]. A drawback of this approach is that it does not lend itself to the scaling up of individual devices into systems. Although nucleation sites can be prescribed by patterning the substrate surface before growth [2], preserving narrow optical line width in these site-controlled dots remains a challenge because patterning the surface invariably introduces defects and impurities that broaden nearby quantum dots’ optical line width. One solution would be to grow a thick buffer of pure GaAs on the patterned surface before nucleating dots; however, the anisotropy in the growth of GaAs tends to fill in or elongate the pattern. Our technique actually takes advantage of this growth anisotropy to evolve an etched pattern of holes and lines into faceted structures in which single dots nucleate. Using this technique, we were able to grow a GaAs buffer layer of up to 90 nm thickness between the processed surface and the dot nucleation surface. Additionally, by varying the spacing between lines in the original pattern, we can change the number of dots nucleating per site from single to a chain of several. Our dots are grown in a Schottky diode structure. Their PL spectrum shows discrete charging transitions, as well as narrow lines on the order of the spectrometer’s resolution limit of 20 micro eV. [1] A. Badolato et al. Deterministic Coupling of Single Quantum Dots to Single Nanocavity Modes. Science 308, 1158 (2005). [2] P. Atkinson, et al. Formation and ordering of epitaxial quantum dots. Comp. Rend. Physique 9, 788 (2008).

      4:00 PM - CC5.07

      Heavy to Light Hole Intersubband Absorption in the Valence Band of GaAs/AlAs Heterostructures

      Mohammed Imrul  Hossain1, Zoran  Ikonic2, John  Watson3, Michael  J  Manfra4, Oana  Malis5.

      Show Abstract

      Intersubband transitions (ISBTs) within the conduction band of semiconductor quantum wells (QWs) have been widely explored, which eventually led to their application in QW infrared photo-detectors and quantum cascade lasers. Compared to electron ISBT there has been considerably less research on the hole ISBT in the valence band (VB), mainly because the VB has a complex structure that makes it more difficult to model. However ISBTs in the VB are interesting because of the optical activity for both in-plane and out of plane light polarization, opening up the possibility of surface-perpendicular emission or absorption. Hole ISBT between different kinds of hole states, i.e. between heavy and light hole states are not subject to the same selection rules as electron ISBT (light emission and absorption restricted to the plane of the semiconductor), therefore allowing light emission and absorption in the direction normal to the semiconductor surface. This may eventually lead to novel optoelectronic devices like vertical cavity surface emitting lasers operating in the mid-infrared range. We report heavy to light (H-L) hole intersubband absorption in the VB of GaAs QWs with AlAs barriers in the mid-infrared range. The samples were grown with atomic layer precision by molecular beam epitaxy. For the p-type doping a high-purity solid carbon source was used. The p-type doping was 1.2×1012 cm-2 for our samples. Previously we reported broad features in the s-polarization and attributed them to H-L hole ISBT. Good agreement was found between the experiment and theory for the mid-infrared heavy to heavy (H-H) hole absorption while the H-L hole absorption experimental values had a poor agreement with the theory. Now we report both strong H-L hole and H-H hole transitions measured with in-plane (s-polarized light) and out of plane (p-polarized light) respectively, for three different QW widths of 42 Å, 51 Å, 59 Å. XRD and TEM scans ensure that the QW widths are within 0.5 Å of the designed values. A multi-pass waveguide geometry was used for the mid-infrared absorption measurements. All the measurements were taken at 77K. For the H-L hole transition in s-polarization the absorption peak varied from 255meV to 175meV for well width variation of 42 Å to 59 Å. In the p-polarization the absorption peak varied from 258 meV to 171 meV over the same well width range. For the H-H transition (p-polarization only) the absorption peak changed from 163 meV to 103 meV over the same width-range. The experimental results were compared with theoretical simulations using the 6x6 k.p model. The effect of inter-diffusion was incorporated in the simulations. The best agreement between theory and experiment was found for an inter-diffusion range of 6 to 10 Å. The comparative study between experimental values and theory provides us with valuable information and insight for future novel devices based on hole ISBTs.

      4:15 PM - CC5.08

      Epitaxial Quantum Dots in the InGaP/GaAsP/(Si) Metamorphic Materials System for Photovoltaic and Optoelectronic Applications

      Tyler  J  Grassman1 2, Javier  Grandal1, Andrew  M  Carlin1, Mark  R  Brenner1, Beatriz  Galiana1, John  A  Carlin3, Limei  Yang2, Michael  J  Mills2, Steven  A  Ringel1 2 3.

      Show Abstract

      Epitaxial Stranski-Krastanov type III-V semiconductor quantum dots (QDs) have found application and research directed toward a number of optoelectronic technologies, including light emitters, photodetectors, and solar cells. The inclusion of such nanostructures provides the ability to effectively tailor the energy of photon emission and/or absorption within device structures. This sort of band gap adjustability can also be achieved via metamorphic (lattice-engineered) materials, which have also recently experienced significant research and application toward the same optoelectronic technologies. As such, the combination of these two approaches is an obvious step on the path to ultimate semiconductor materials tunability. The vast majority of III-V QD work to date has utilized standard substrate materials (e.g. GaAs, InP) as the host, thereby somewhat limiting their applicability, while lattice-engineered materials have seen comparatively little attention, save for a few reports concerning InAs QDs on InxGa1-xAs. However, recent developments in the growth of GaP on Si, and subsequent GaAsyP1-y metamorphic buffers, have helped make accessible the wide range of band gaps with photovoltaic and optoelectronic applicability available between the Si and GaAs lattice constants, with the added advantage of direct, monolithic integration with Si substrates and devices. We will present here work focused on MBE-based growth and characterization of QD nanostructures within metamorphic GaAsyP1-y matrix materials. The objective of this effort is the understanding of how pre-existing dislocations and characteristic surface cross-hatch in metamorphic materials affects the nucleation and growth of epitaxial QDs, as well as strain-compensation of encapsulated QD arrays. Initial exploratory experiments on the nucleation of InGaAs QDs on photovoltaic-relevant GaAs0.90P0.10 host materials, grown on both GaAs and Si substrates, confirmed, by AFM, the formation of dense arrays of self-assembled QDs, even in the presence of a pre-existing threading dislocation density and surface cross-hatch. 20-layer periodic encapsulated QD structures exhibited strong low-temperature PL emission 400 meV blue-shifted from the bulk emission wavelength due to the quantum confinement effect. TEM imaging shows that the QDs are vertically aligned, although tilted away from surface normal, indicating that the dislocation network does not substantially interrupt the strain-induced alignment observed in non-metamorphic QD systems. Further work, currently in progress, will be presented regarding the further refinement of the InxGa1-xAs/GaAs0.90P0.10 based QD/matrix system, as well exploration of other potentially useful materials combinations, including GaAsyP1-y and InzGa1-zP QD materials capable of visible light emission, including the elusive green wavelengths.

      4:30 PM - CC5.09

      Engineering the Morphology and Optical Properties of InP-based InAsSb/InGaAs Nanostructures via Sb Exposure and Graded Growth Techniques

      Wen  Lei1 2, Hoe  Tan1, Chennupati  Jagadish1.

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      Semiconductor InAsSb/InGaAs/InP nanostructures (quantum dots and quantum wires) are promising candidate materials for fabricating mid-infrared (2-3 um) emitters, which have a wide range of applications in military, telecommunications, molecular spectroscopy, biomedical surgery, environmental protection and manufacturing industry, etc. Some work has been devoted to growing self-assembled InAsSb quantum dots and extending their emission wavelength. However, it still presents a big challenge to achieve high quality InAsSb nanostructures with controlled morphology and optical properties due to the large lattice mismatch between InAsSb and InP, surfactant effect of Sb atoms, and low growth temperature requirement for Sb compounds. In this work, two novel growth techniques (Sb exposure and graded growth) are applied to realize the control over the morphology and optical properties of InAsSb nanostructures. As for the technique of Sb exposure, the surface of InGaAs buffer layer is exposed to trimethylantimony precursor flow before the growth of InAsSb nanostructures. As a result, the surface/interface energy in the system is reduced, while the strain energy in the system is enhanced, which leads to a shape transition from dot to dash, and to wire for the InAsSb nanostructures with increasing the Sb exposure time. Consequently the linear polarization degree of the photoluminescence emission from the InAsSb nanostructures increases as a result of the shape change of the nanostructures. In addition to Sb exposure, graded growth of InAsSb nanostructures is also explored to control their morphology and optical properties. The nominal composition of As / Sb was graded linearly from a starting value to a ending value during the deposition of InAsSb while keeping the total As and Sb constant. It is found that the actual Sb composition in InAsSb nanostructures increases with increasing the initial Sb composition during the graded growth, which can be explained by the different sticking coefficients of As and Sb atoms. As a consequence of the change of actual Sb composition, the shape of the InAsSb nanostructures evolves from circular dots to elongated dots, to dashes and then to wires with increasing initial Sb composition during the graded growth. Accompanying this shape change is a narrower height distribution due to the decrease in their average height. Compared with InAsSb nanostructures obtained with lower initial Sb compositions, the InAsSb nanostructures fabricated with higher initial Sb composition present a larger linear polarization degree and smaller red-shift rate with temperature in their photoluminescence emission. This research demonstrates two technologically important techniques, Sb exposure and graded growth, to engineer the morphology and physical properties of InAsSb nanostructures, the principle of which can also be applied to other material systems.

      4:45 PM - CC5.10

      Quantum Dot Molecules: Controlled Formation of Molecular States in Different Quantum Dot Geometries

      Matthew  Doty1, Weiwen  Liu1, Xinran  Zhou1, Allan  Bracker2, Dan  Gammon2, Gregory  Salamo3, Zhiming  Wang3, Jihoon  Lee4.

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      Quantum Dot molecules are created when coherent tunneling of electrons or holes creates molecular orbitals delocalized over multiple quantum dots. The delocalized molecular states can have a variety of unique new optical, electronic and spin properties of interest for future device applications. These properties can be engineered with molecular structure by changing the spatial extent and material compositions over which the molecular states are delocalized. We will present recent results on the experimental observation of delocalized molecular states and charge interactions in lateral quantum dot molecules. We will compare and contrast these results with the more firmly established understanding of charge and spin interactions in vertical quantum dot molecules, emphasizing the ways in which different quantum dot geometries create different molecular interactions and properties.

      CC6: Poster Session: Optical Materials and Devices II

      • Tuesday PM, November 27, 2012
      • Hynes, Level 2, Hall D
       

      8:00 PM - CC6.01

      Low Temperature Synthesis of Blue Emitting InP/ZnS Quantum Dots

      Kipil  Lim1, Ho Seong  Jang1, Kyoungja  Woo1.

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      Semiconductor nanoparticles, quantum dots (QDs), present unique physical properties due to quantum confinement effect when the size of particles is less than exciton Bohr radius. Recently the semiconductor materials with non-toxic elements attract great interest for the application to the industry, such as light emitting diodes, bio imaging and photovoltaic devices. InP semiconductor QDs are one of non-toxic materials and attract attention due to its strong luminescence and appropriate bandgap for visible light emission. Herein, we present the synthesis and characterization of blue emitting InP core /ZnS shell QDs, which were hard to obtain by conventional methods. The synthesis of small QDs is necessary in order to acquire InP QDs with higher bandgap. We dropped the temperature drastically after mixing of the In and P precursor to synthesize small QDs. Not only did we minimize the initial size of InP core, we could further control the size of InP core through etching by residual acetic acid at three different growth temperatures. Thereby, we synthesized the InP core QDs, whose band edge absorptions are 425 nm, 438 nm, and 456 nm with the increasing growth temperature. Luminescent intensity and stability can be increased if InP cores are encapsulated by ZnS shell material. It is important that the size of InP cores remain unchanged during formation of the ZnS shell. By reducing shell synthesis temperature, we could successfully attain blue (475 nm), greenish-blue (485 nm), and bluish-green (497 nm) emitting InP core /ZnS shell QDs. Three colors of InP core /ZnS shell QDs emitting at 475 ~ 497 nm pointed on the CIE 1931 chromaticity diagram will be presented, together with the TEM, XRD, XPS, and spectroscopic analysis.

      8:00 PM - CC6.03

      1D ZnO Nanoarray Using Electron Beam Lithography (EBL)

      Chandan  B  Samantaray1, Meric  Arslan1, Hareesh  Dondapati1, Dipti  Biswal1, Tionne  Birdsong1, Aswini  K  Pradhan1.

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      1D array of ZnO nanorods (NRs) have been attracted much attention for nanoscale sensors, detectors, and optoelectronics devices. Electron beam lithography (EBL) is one of the most versatile nanofabrication tools of making patterns on seed layer that has enabled the growth of periodic ZnO nanostructures. In case of EBL, the primary electron beam has either forward or back scatter as approached towards the resist coated substrates. The total electron yield (σ) which is the sum of the above depend upon the accelerating voltage that is being used. Generally, higher accelerating voltage (σ <1) induces negative charges and the lower one (σ >1) makes it positively charged. As ZnO has negative charged carriers in majority, surface attachment supposed to be hindered at the higher voltage and conversely enhanced at the lower one. Here we have prepared Al: doped ZnO (AZO) seed layers of ~280 nm thick on the glass substrate using RF magnetron sputter at an ambient of 3500C. The AZO layer on glass was spin coated with ~50 nm of PMMA (Mol. wt. 950K) and post baked at 1800C for 2 mins. The samples were then patterned using EBL at different beam energies of 2, 5, 10, and 20 keV. After the patterning, the resist was undergone development in Methyl-isobutyl-ketone and isopropyl alcohol (MiBK+IPA) at a ratio of (1:3) for 30 sec, rinse in IPA for 15 sec, and then dried N2. Patterned samples were processed for ZnO nanorods growth using hydrothermal technique in a solution of Zn (NO3)2 and hexamethylenetetramine (HMT) at 900C for 4 hrs. After successive NRs growth, the unexposed PMMA were lifted-off using N-methyl-2-pyrrolidinone (NMP) for 10 mins at 600 C. Then samples were rinsed in DI and dried in nitrogen, and ready for FESEM imaging. In order to make 1D nano-array, the solid attachment of ZnO NRs on to the patterned surface is essential. Especially, at higher beam energy (~ 20 keV), the incident electron beam decelerates due to the accumulated negative charges that already built on the surface in due course of irradiation. This causes a negative shielding potential close to the surface at micron level, and completely unfavorable for the ZnO attachment. However, at a comparatively lower beam energy (~ 5 keV or less), the secondary electrons (SE) are responsible for the pattern with the irradiation zone centered by the local positive field. Therefore, the negatively charged ZnO NRs can be controlled at lower voltages easily and also put site-selective at increasing the dose. This work is supported by the DoD (CEAND) Grant Number W911NF-11-1-0209 and W911NF-11-1-0133 (US Army Research Office), NSF-CREST (CNBMD) Grant number HRD 1036494 and NSF-RISE Grant number HRD-0931373.

      8:00 PM - CC6.04

      Photoinduced Charge Separation and Energy Transfer from Semiconductor Quantum Dots for Solar Energy Conversion

      Shengye  Jin1 2, Gary  P.  Wiederrecht1 2, Alex  B. F.  Martinson4 2, Joseph  T.  Hupp3 2.

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      Semiconductor quantum dots (QDs) are of great interests for their unique photophysical properties including tunable and broad spectral responses (visible to near IR), high luminescent quantum yields, long exciton lifetimes and ultrafast interfacial charge separation dynamics. These properties make QDs an attractive material with numerous potential applications in solar energy conversion. The photoinduced charge separation and energy transfer dynamics in QDs are among the key processes that control the efficiency of harvesting and converting sunlight into electricity (or fuels) using QDs. This presentation/poster introduces the fundamental studies about interfacial charge separation and energy transfer dynamics from QDs. These studies target important scientific questions such as the role of surface defects in charge separation, the ultrafast dynamics in highly reductive QDs, and strategies of utilizing QDs for more effective sunlight harvesting, paving the road for practical applications of QDs in solar energy conversion.

      8:00 PM - CC6.05

      Enhancing Light Emission of ZnO Microwire-based Diodes by Piezo-phototronic Effect

      Qing  Yang1 2, Ying  Liu1, Zhong  Lin  Wang1.

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      Light emission from semiconductors depends not only on the efficiency of carrier injection and recombination but also extraction efficiency. For ultraviolet emission from high band gap materials such as ZnO, nanowires have higher extraction efficiencies than thin films, but conventional approaches for creating a pn diode result in low efficiency. We exploited the noncentral symmetric nature of n-type ZnO nanowire/p-type GaN substrate to create a piezoelectric potential within the nanowire by applying stress. Because of the polarization of ions in a crystal that has noncentral symmetry, a piezoelectric potential (piezopotential) is created in the crystal under stress. The piezopotential acts as a “gate” voltage to tune the charge transport and enhance carrier injection, which is called the piezo-phototronic effect. We propose that band modification traps free carriers at the interface region in a channel created by the local piezoelectric charges. The emission intensity and injection current at a fixed applied voltage have been enhanced by a factor of 17 and 4, respectively, after applying a 0.093% compressive strain and improved conversion efficiency by a factor of 4.25. This huge enhanced performance is suggested arising from an effective increase in the local “biased voltage” as a result of the band modification caused by piezopotential and the trapping of holes at the interface region in a channel created by the local piezoelectric charges near the interface. Our study can be extended from ultraviolet range to visible range for a variety of optoelectronic devices that are important for today’s safe, green, and renewable energy technology. Reference: Qing Yang,Wenhui Wang,Sheng Xu,and Zhong Lin Wang, Nano. Lett., 11 (2011) 4012

      8:00 PM - CC6.06

      Dynamic Color Changes in Polymer Stabilized Cholesteric Liquid Crystals

      Michael  E.  McConney1, Vincent  P.  Tondiglia1, Lalgudi  V.  Natarajan1, Timothy  J.  White1, Timothy  J.  Bunning1.

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      Cholesteric liquid crystals (CLCs) are attractive photonic materials for their ease of fabrication and their dynamic properties. Typically CLCs with a positive dielectric anisotropy are used in dynamic photonic switching applications, where an AC field across a cell causes a change from a colored reflective state to a clear state. On the other hand, negative dielectric CLCs find very little use due to the fact that applied fields cause no rearrangement of the anisotropic molecules in a typical planar aligned liquid crystal cell. Here we present unique dynamic coloration effects caused by broadening and tuning of the selective reflection in polymer-stabilized CLC’s with a negative dielectric ansitropy under DC electric fields. Large scale wavelength changes of several hundred nm can be induced at low field strengths. The mechanism of this previously unreported approach to dynamic color change are explored in this talk.

      8:00 PM - CC6.07

      Optical Properties of a Bragg Lattice and Random Array of Plasmonic Nanoparticles in AlGaAs

      Vladimir  V.  Chaldyshev1, Vitalii  I  Ushanov1, Valerii  V  Preobrazhenskii2, Mikhail  A  Putyato2, Boris  R  Semyagin2.

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      Plasmonic nanoparticles embedded into a dielectric matrix create an interesting optical medium, where the features related to the plasmon resonance can be shifted to visible or even infrared range. Generally, the optical properties of such medium can be tailored by variation of size and spatial distribution of the nanoparticles as well as by the chemical composition of the metal inclusions and of the dielectric host. We report results of our study of the optical properties of metamaterials consisting of a crystalline AlGaAs matrix, where metallic nanoparticles were created by the process of self-organization. The driving force for the self-organization was supersaturation of the matrix by group-V elements, which was achieved by special growth conditions in molecular beam epitaxy. In undoped AlGaAs the plasmonic nanoparticles were pure As with hexagonal structure and almost spherical form. Doping the matrix with Sb allowed us to produce nanoparticles of AsSb alloy. In both cases the spatial distribution of the nanoparticles was random. Patterning of the spatial distribution of the AsSb nanoparticles was achieved when we utilized local delta-doping with Sb instead of the uniform doping. Our study shows a weak influence of the random system of the As nanoparticles on the optical properties of the AlGaAs films, since the plasmon resonance in such particles does not match the transparency window of the AlGaAs matrix. Alloying of As with Sb shifts the plasmon resonance toward lower energies. As a result the AlGaAs medium with a random system of the AsSb nanoparticles becomes opaque. This process is governed the Mie scattering and absorption. The spatially ordering of system of the AsSb nanoparticles drastically changes the optical properties of the medium, giving rise to a Bragg resonance. The magnitude of the Bragg resonance appears to be as strong as 40% of reflectivity with the total volume fraction of the metallic nanoinclusions being well below 1% and with 12 periods in the Bragg sequence.

      8:00 PM - CC6.08

      Near-field Optical Spectroscopy of Exitonic States in Single InAs Quantum Dots Grown by Molecular Beam Epitaxy on Vicinal Surfaces

      Alexander  Senichev1, Vadim  Talalaev1 2, Joerg  Schilling2, Alexei  Bouravleuv3 4, George  Cirlin3 4 5, Peter  Werner1.

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      The development of the effective optoelectronics devices for the quantum information technology requires creation of a new type of light sources. Such sources have to emit carefully controlled number of photons with minimal timing jitter. Self-assembled InAs quantum dots (QDs) offer the high potential for the realizing single photon and entangled photon sources. The most common technique for growing self-assembled QDs is the Stranski-Krastanov (SK) method. However, a high density of InAs QDs in case of SK growth mode limits the study of optical properties of single QD by measurements of an ensemble of QDs. In this work we report on the formation of QDs structures of low density and appropriate size. The QDs structures were grown by molecular beam epitaxy in subcritical regime, as the InAs layer thickness (1.4 ML - 1.6 ML) was below critical thickness for SK mode. For additional spatial separation of QDs we introduced the growth on misoriented (vicinal) GaAs substrates. For the optical characterization we applied a near-field spectroscopy of such low density arrays of InAs QDs required for addressing single quantum dots. Low-temperature near-field scanning optical microscope (NSOM) operating at a temperature of 10 K inside a high vacuum chamber was used (spatial resolution < 0.2 μm). NSOM allows us to get the information about the spatial position of QDs and record corresponding optical spectra. With the NSOM technique appropriate QDs were accurately selected for detailed study an ensemble of sharp lines, originating from the emission of different excitonic states. Based on excitation power dependencies of these sharp lines intensity exitonic states were specified.

      8:00 PM - CC6.09

      Optical Response of Bismuth Nanoparticles: Potential for Sensing and Switching Applications

      Johann  Toudert1, Rosalia  Serna1, Miguel  Jiménez de Castro1.

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      Bismuth is a low toxicity heavy element with a low melting point, presenting peculiar physical properties. In the bulk state, it is classified as a semi-metal and presents a particularly high electron mean free path, low effective mass and long De Broglie wavelength. These exciting features have stimulated research that evidences confinement effects on the electronic response of nano-bismuth structures, such as thin films, nanowires or nanoparticles. In contrast, the optical response of nano-bismuth under the form of nanoparticles remains unexplored so far, despite of its demonstrated potential for thermo-optical sensors and switches [1]. In this work, we provide experimental evidence of the strong sensitivity of the optical response (from the near UV to the near IR) of bismuth nanoparticles to their size, shape and organization. At such aim, tailor-made 2D assemblies of bismuth nanoparticles presenting different characteristic nanoparticles size, shape and organization, and sandwiched between thin amorphous aluminium oxide layers, were prepared by pulsed laser deposition. This structure constitutes a robust nanocomposite system for reliable structural studies and for experimental assesment of the bismuth nanoparticles optical response. Furthermore, from static and dynamic optical calculations, we have investigated the electronic mechanisms (plasmon excitation and damping mechanisms) driving the topology-sensitive optical response of the bismuth nanoparticles. Finally, we propose a roadmap to the elaboration of nano-bismuth-based thermo-optical sensors and switches with maximized optical contrast. [1] E. Haro-Poniatowski, R. Serna, M. Jiménez de Castro, A. Suárez-García, C. N. Afonso and I. Vickridge, Nanotechnology 19, 485708 (2008) Acknowledgements: This work has been supported by the EU under project FP7-NMP-2010-Eu-Mexico Grant Agreement no. 263878: Functionalities of Bismuth based Nanostructures (BisNano), by the Spanish CICYT under project MAT2009-14369-C02-02, and by CSIC- CONACYT-2008MX0050 collaborative action. J. T. acknowledges a Juan de la Cierva Grant JCI-2009 - 05098.

      8:00 PM - CC6.11

      Optimizing the Multilayer InAs/GaAs Quantum Dot Heterostructure to Produce Bilayer like Uniformity by Using Annealing and Variable Spacer Thicknesses for Long Wavelength (1.3µm or 1.55 µm) Applications

      Subhananda  Chakrabarti1.

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      Dedicated research on self-assembled InAs/GaAs quantum dots (QDs) has been triggered due to their inherent capability to extend emission of GaAs-based optical devices to long wavelengths such as 1.3 or 1.55 µm. Bilayer QD heterostructures are an apt solution to the major obstacle of large PL linewidth. But increasing QD density and simultaneously maintaining uniformity of QD heterostructures is a big problem. By stacking multilayer of QDs by Stranski-Krastanov growth we can solve these problems but the strain built-up and consequent relaxation of strain by dislocation formation is uncalled for. Thus, keeping all aspects in mind we would like an extension of bilayer QD structure into multilayer coupled structure which is the primary focus of this study. A comparison study of the bilayer sample a with the multilayer samples (b and c) is made by varying the barrier width between the stacked QD layers in samples b (11 nm) and c (12.5 nm) and maintaining other parameters same. Large QDs were grown at a very low growth rate to achieve the 1.3um emission target. Due to larger dots, strain is created in the spacer layer resulting in intrinsic dislocations. The thin GaAs spacer induces electronic and strain coupling creating non radiative recombination centers and broadening the linewidth. It was observed that sample c has much higher IPL and activation energy than that of sample b indicating lesser dislocations due to a relatively thicker spacer layer. Moreover the FWHM of sample c was lesser than that of sample b indicating better homogeneity in the dots. The peak intensity and line width of all the samples were significantly improved by annealing which in turn increases the modal gain of lasers and absorption coefficient of photodetectors. There is clear evidence that the amount of In-Ga intermixing induced by annealing is dependent on the QD size. The larger dot compared to the smaller dot will have lesser hydrostatic strain which induces greater In-Ga intermixing in the vertical direction resulting in more blue shifting. This decreases the energy difference between the shifted dots, making the linewidth narrower. The integrated PL intensity of sample c annealed at 750°C is much better than that of sample a and the FWHM is also nearly the same which serves the purpose of our study to extend the bilayer into the multilayer. The temperature dependent PL spectra showed that the peak intensity of the larger dots increased upon increasing the temperature till 140K while that of the smaller dots decreased. This is attributed to tunneling of the electrons from the smaller QDs to the larger QDs on increasing the temperature due to the lower confinement energy of the larger QDs. It is clear from this study that strain patterning is necessary for the development of multilayer QD heterostructures with the same homogeneity as that of bilayers. Annealing can be effective in improving the homogeneity and reducing intrinsic defects. Acknowledgement: DST, India

      8:00 PM - CC6.12

      Hetero-epitaxial Growth Process of Type-II GaSb/GaAs Quantum Dot System by Metal-organic Molecular Beam Epitaxy

      Katsuhiro  Uesugi1, Masataka  Sato1, Kohei  Miyazawa1, Takanari  Yumi1.

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      GaSb/GaAs type-II quantum dots have attracted much attention for new optoelectronic devices at long wavelengths, where only holes are confined in dots. However, it is an issue that it is easy to produce the Sb segregation and As-Sb compositional intermixing during the hetero-epitaxial growth, because the bonding strength of Ga-Sb is weak compared with that of Ga-As. In the case of MOMBE using TDMAAs and TDMASb precursors, the etching of GaSb dots was caused by the supply of these precursors at high temperature. Then the blue shift of wavelength arises by the reduction in dot size or Ga-As mixing. To realize long-wavelength emission of GaSb/GaAs dots, it will be important to study the growth process of GaAs cap-layer to bury GaSb dots. In this paper, we examine the hetero-growth processes of GaSb/GaAs dot system using MOMBE. We propose 2-step growth of GaAs cap-layer and demonstrate the longer wavelength emission in GaSb/GaAs dots. GaSb/GaAs dots were grown on semi-insulating GaAs(001) substrates using MOMBE. MO precursors used were TEGa, TDMAAs, and TDMASb. GaAs surfaces were cleaned at 570oC with the simultaneous supply of TDMAAs and then a 100-nm-thick GaAs buffer layer was grown at 540oC. After cooling down to the growth temperature of GaSb, TDMASb was supplied to the (2x4)-GaAs surface. Then GaSb dots were grown on the Sb-terminated (1x3) surface in the Stranski-Krastanow growth mode. The dot formation was identified by the change of RHEED patterns. After the growth of GaSb dots, a 30-nm-thick GaAs cap-layer was grown at the temperature of 400~510oC. The hetero-growth processes of GaAs cap-layers were evaluated by RHEED and AFM observations. Photoluminescence (PL) properties of the GaSb/GaAs dots were measured at 20 K. Typical GaSb dot size grown at 480oC was 8 nm in height and 70 nm in width. By the irradiation of TDMAAs, the etching of dots was clearly observed at >430oC. Although the flattened out of the growing surface was observed during GaAs cap growth above the temperature of 430oC, PL peak wavelength of the GaSb dots was blue-shifted by the increase of the GaAs growth temperature. Since the disappearance of the GaSb dots was not observed by the TDMAAs supply at <430oC, GaAs cap-layer was grown at 400oC. At the initial growth of GaAs layer, dot structures were formed on the terrace region between GaSb dots. Red-shift of PL peak was observed, but luminescence efficiency of dots was decreased due to the degradation of crystalline quality of the cap-layer. To improve the luminescence efficiency, 2-step growth of GaAs cap-layer was done. After GaAs dots were grown on the terrace between GaSb dots at 400oC, the GaAs cap-layer was grown at 450oC to bury the GaSb and GaAs dot structure. The red shift of the luminescence peak up to 1.2 µm and the improvement of luminescent efficiency of GaSb dots were observed.

      8:00 PM - CC6.13

      Structural and Optical Characterization of InxGa1-xN Quantum Wells with Atomic and Sub-wavelength Resolutions

      Kamal  Hussain  Baloch1 2 3, Aaron  Johnston-Peck2, Kim  Kisslinger2, Xiang  Zhou1 3, Eric  Jones3, Parijat  Deb4, Eric  Stach2, Silvija  Gradecak1 3.

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      The future of lighting will likely be tied to solid-state light emitting diodes (LEDs) because they are more efficient, environmentally friendly, and cost-effective compared to traditional light sources. InGaN compounds are of particular interest for solid state lighting because of their potential to emit light over the entire visible spectrum. During the past decade, attempts have been made to understand the carrier dynamics in InGaN multiple quantum wells utilized as the active light-emitting material in LEDs; given the small dimensionality of the quantum wells, transmission electron microscopy (TEM) has been extensively used to study their structural and chemical uniformity. Several TEM studies showed that strain induced in InGaN due to lattice mismatch and the miscibility gap between InN and GaN cause formation of In-rich clusters- the presence of which has been argued, by some, to be crucial for the superior performance of these materials [1]. In contrast, separate studies have suggested that these In-rich clusters are an artifact of TEM imaging caused by electron irradiation [2] and have no effect on a device’s performance. Towards this end, we employ aberration-corrected (Cs) TEM to image a series of InGaN samples including those from reference 2 with atomic resolution at energies and doses below the knock-on threshold. We have systematically shown that operating Cs-TEM at 120 kV inhibits knock-on damage without compromising the atomic resolution. Low-loss electron energy-loss spectroscopy and Cs-corrected scanning TEM (STEM) data complement our TEM findings. Additionally, a unique cathodoluminescence-STEM setup has enabled us to directly correlate structural and optical properties of our samples. This work furthers understanding of structural features that underpin the carrier dynamics in InGaN quantum wells and will help towards further optimization of these structures. [1] J. R. Jinschek et al., Solid State Comm., 137, 230-234 (2006) [2] T.M. Smeeton, C.J. Humphreys, J.S. Barnard, et al., J. Mater. Sci. 41 2729 (2006)

      8:00 PM - CC6.14

      Solar Energy Conversion with Tunable Plasmonic Nanostructures

      Ran  Long1, Yujie  Xiong1.

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      Harvesting energy directly from sunlight is increasingly recognized as an essential component of future global energy production. In this presentation, I will demonstrate the applications of surface plasmon in the conversion from solar energy to electricity and chemical energy along two different mechanisms. In our work, the surface plasmonic features of metallic nanocrystals are tuned by tailoring their size, shape, structure and composition in solution-phase synthesis. In turn, these tunable plasmonic nanostructures are implemented in solar energy conversion in two example systems. In the first system, we demonstrate that the photothermal effect of silver nanostructures can provide a heat source for thermoelectric devices, which serves as an important supplement to plasmonics-enhanced photovoltaic devices. In the second case, we have explored the role of sunlight in organic reactions that are catalyzed by a class of newly-designed bimetallic nanocrystals. It is expected that the present work will enable us to expand the applications of surface plasmonics and open the door to new concepts of solar energy conversion.

      8:00 PM - CC6.15

      Nanoantenna for Direct Solar Energy Extraction

      Jing Sheng  Pang1, Peter  Gammon2, Evgeniy  Donchev1, Fang  Xie1, Anthony  Centeno3, Peter  K  Petrov1, Mary  P  Ryan1, Neil  Alford1.

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      The optical rectenna consists of two main parts: a nanoantenna that absorbs the incoming photons, converting them to electrical current and a rectifying diode. To harvest the solar energy efficiently the key parameter is the absorption efficiency of the nanoantenna at optical frequencies. In this work, gold and silver metallic nanoparticles were used to fabricate the antenna nanostructures because their absorption wavelength, corresponding to their localised surface plasmon resonance, can be effectively tuned in the visible and infrared region. These structures also play a critical role in the metal-insulator-metal (MIM) diode structure. Various structures of optical rectenna have been fabricated using a combination of nanosphere lithography, oxygen plasma treatment and argon ion-milling process. In the first approach a mono-layer of polystyrene nano-spheres was deposited onto the top of a silicon substrate that had been pre-coated with a layer of metal and an ultra-thin oxide layer. This was achieved by dipping the substrate into a solution containing nanospheres with diameter of 300 nm or 620 nm, and withdrawn either vertically or at an angle. This layer of polystyrene then served as a mask for metal deposition, thus creating nanotriangle-type nanostructures as the top MIM contact. In the second approach a polystyrene mask was deposited on top of fully-formed MIM layers, before defining etched structures using an Argon ion-milling process. By varying the energy and the angle of incidence of the Argon ions during the milling process, aligned nanorods, nanodiscs, and nanopencils were produced. To form smaller diameter structures, the polystyrene sphere size was reduced post deposition using an oxygen plasma. Integrating sphere, UV-Vis and Fourier transform infrared spectroscopy (FTIR) were used to measure the optical properties of these nanoantenna. The electrical properties were tested with conductive atomic force microscopy (c-AFM). The results will be presented and discussed in the context of optimised solar absorption.

      8:00 PM - CC6.18

      Genetic Optimization of Optical Nanoantennas

      Carlo  Forestiere1 2, Antonio  Capretti1 2, Jacob  Trevino1, Antonello  Tamburrino3, Giovanni  Miano2, Luca  Dal Negro1.

      Show Abstract

      Metal nanostructures can act as plasmonic nanoantennas (PNAs) due to their unique ability to concentrate light over sub-wavelength spatial regions. However engineering the optimum PNA in terms of a given quality factor or objective function has been a challenge due to the large number of geometrical parameters involved. We propose a novel design strategy of PNAs by coupling a genetic algorithm (GA) to the analytical multi-particle Mie theory. The positions and radii of a metallic nanosphere clustes are found by requiring maximum electric field enhancement at a given focus point. Within the optimization process we introduced several constraints in order to guarantee the physical realizability of the tailored nanostructure with electron-beam lithography (EBL) Aiming at modeling a realistic device based on a bow-tie antenna and on an underlying substrate, we used the GA approach discussed above to obtain an initial solution, which was then refined by using a full vector three-dimensional finite-difference time-domain (3D FDTD) simulator. Our GA optimization results unveil the central role of the radiative coupling in the design of PNA and open new exciting pathways for the engineering of metal nanostructures. Samples are fabricated using Electron Beam Lithography and surface-enhancement Raman scattering measurements were performed in order to validate the theoretical predictions.

      8:00 PM - CC6.19

      Two-plasmon Quantum Interference

      James  S.  Fakonas1, Yousif  Kelaita1, Harry  A.  Atwater1 2.

      Show Abstract

      Surface plasma waves are typically quantized by direct analogy to electromagnetic waves in free space or in dielectric media. As a result, the quantum theory of these waves predicts that their quanta—surface plasmons—should exhibit the same quantum phenomena that photons do. Experiments that test this analogy have begun only relatively recently, however, and it remains to be seen just how faithfully surface plasmons reproduce the quantum behaviors of their free-space counterparts. In this work, we study the plasmonic analog of two-photon quantum interference (TPQI), also known as the Hong-Ou-Mandel effect. In free-space TPQI experiments, photons that arrive simultaneously at adjacent inputs of a 50-50 beam splitter are always observed to exit the splitter together in one output port or the other, but never in separate outputs. Quantum theory explains this result as a consequence of destructive interference between the probability amplitudes of two processes: one in which both photons are transmitted and the other in which both are reflected. Importantly, TPQI requires that the two photons be as nearly indistinguishable as possible; any distinguishing information tends to reduce the visibility of the effect. We investigate TPQI in waveguides that involve plasmonic elements. We generate pairs of single photons at 810 nm by spontaneous parametric down-conversion of light from a 405 nm diode laser, collect them into optical fibers, and couple them into sub-micron silicon nitride waveguides, which deliver them to and collect them from various configurations of dielectric-loaded surface plasmon polariton waveguides and couplers. In particular, we consider a structure in which a plasmonic directional coupler plays the role of the 50-50 beam splitter in traditional TPQI measurements and similar structures in which plasmonic waveguides are inserted before one or both inputs of a dielectric 50-50 directional coupler. We study the effects of these plasmonic elements on the visibility of TPQI and comment on the roles of dispersion and loss.

      8:00 PM - CC6.20

      Efficiency of Plasmonic Hot Carrier Emission Devices: Correlated or Uncorrelated Plasmons and Electrons?

      Andrew  Jay  Leenheer1, Prineha  Narang1, Harry  A  Atwater1.

      Show Abstract

      The decay of surface plasmon resonances into hot electron-hole pairs has recently been utilized in Schottky barrier optical detectors and energy conversion devices, in contrast to many applications where damping is to be ardently avoided. Proposed devices include resonantly-enhanced infrared sensors, sub-bandgap light absorption in photoelectrochemical cells, and metal-absorber power conversion. However, such devices are subject to the physics governing internal photoemission and thermionic emission, and for practical applications the quantum efficiency is an important parameter to consider. Here, we couple optical finite-element simulations of such devices to a model for hot-carrier collection efficiency and compare calculations to experiment for plasmonic antenna/Schottky barrier geometries. The main system considered consists of Au electric dipole optical antennas on Si as a Schottky barrier infrared detector, as previously demonstrated. We first calculate the spatial profile of light absorption in the antenna to estimate the spatially-resolved hot-electron generation rate, and then calculate the emission of plasmonically-generated hot electrons over the Au/Si Schottky barrier, considering electron-electron and electron-phonon scattering, the energy distribution of hot electrons, reflections at interfaces, classical emission over the energy barrier, and the limited escape cone arising from the critical normal momentum requirement. In general the efficiency is low due to the small escape cone for energies near the barrier energy. The presence of a Ti adhesion and damping layer is examined in detail as well as possible dielectric layers to enhance scattering. If we assume that carrier excitation is nondirect so as to decorrelate the electron momentum distribution with the original plasmonic electric field, the maximum external quantum efficiency is limited to values around 1% on resonance. Experimental results will also be presented comparing various geometries to simulation with the goal of optimizing efficiency. The possibility of solar energy conversion devices is also analyzed. In this case the diode must be operated in forward bias, and the thermionic emission current is a major detriment. Considering the power conversion efficiency as a function of barrier energy, the best-case values (total solar absorption in a 10 nm thick metal film) are limited to around 0.3% at room temperature. Increasing the maximum efficiency of such devices requires correlation of the plasmon electric field with the hot carrier electron momentum to relax the escape cone constraints to carrier injection efficiency. Models for correlated and uncorrelated electron distributions will be compared to experimental measurements for Au/Si hot carrier injection quantum efficiency as a function of electric field wavevector and polarization.

      8:00 PM - CC6.21

      Generalized Close-packed Honeycomb Plasmonic Antenna Array

      Rustu  Umut  Tok1, Kursat  Sendur1.

      Show Abstract

      Plasmonic antennas operating over a wide spectrum with unidirectional patterns are essential for emerging plasmonic-photovoltaic applications. While promising, spectral engineering of close-packed honeycomb plasmonic antennas with unidirectional absorption is challenging due to the large number of morphological parameters within a Wigner-Seitz unit cell, particle coupling, and interaction between neighboring unit cells. In this study, we introduce morphological parameters within the Wigner-Seitz unit cell to propose a generalized close-packed honeycomb array. The proposed morphological parameters provide additional flexibility for manipulating the spectrum by relaxing geometrical restrictions due to a strong correlation between unit-cell and nanoparticle morphology. In addition, we achieve spectral broadening by breaking the symmetry within a Wigner-Seitz unit cell on a hexagonal grid, rather than breaking the symmetry of the hexagonal grid itself. We demonstrate the advantages of close-packed arrays in terms of spectral response, field enhancement, directionality, and absorption over large surfaces.

      8:00 PM - CC6.22

      Template Stripped Asymmetric Nanostructures for Photovoltaics

      Kevin  M  McPeak1, Mohamad  Hojeij4, Mark  Blome2, Nicolas  Wuersch5, Sven  Burger2 3, Yasin  Ekinci4, David  J  Norris1.

      Show Abstract

      Asymmetric nanostructures can result in interesting optical phenomena. Fabricating these nanostructures over large areas presents significant challenges. Template stripping is a technique that relies on the weak adhesion between coinage metals (Au, Ag, Cu) and SiO2 (e.g. native oxide covered silicon) to provide ultrasmooth surfaces. We report on the fabrication of ultrasmooth asymmetric nanostructured films from both metal and oxide materials over cm2 areas on both flexible and rigid substrates using template stripping. We show how these films can be incorporated as the back reflector in various solar cell devices resulting in enhanced light trapping effects. Both theoretical and experimental results will be presented and comparisons will be made with symmetric nanostructures.

      8:00 PM - CC6.23

      Suppressing Photobleaching with Plasmonic Nanostructures

      Yongmin  Liu1, Hu  Cang1, Yuan  Wang1, Xiaobo  Yin1 2, Xiang  Zhang1 2.

      Show Abstract

      Photobleaching, an irreversible light-induced chemical reaction, changes the structure of a fluorescent molecule and permanently destroys the molecule’s fluorescence capability. It imposes a fundamental limit of the total number of photons that one can harvest from the molecule. Considerable effort has been devoted to suppress the photobleaching, which culminates primarily in chemical-based strategies: making the local environment more chemically inert to fluorophores, or modifying the structure and energy landscape of the fluorophores to be more resistant to photobleaching. Here, we demonstrate that the strong Purcell effect of a plasmonic nanostructure could effectively steer a fluorophore away from photobleaching and prolong a fluorophore’s lifespan, offering a “physical” approach to manipulate the photochemical reactions of bleaching. The underlying mechanism lies in the fact that the two channels—the relaxation and the bleaching— compete with each other during fluorescence process. As a result, we can reduce the probability of the molecule entering the bleaching channel by enhancing the relaxation process with plasmonic structures. Experimentally, up to 1,000 folds more photons have been harvested from a single fluorescent molecule located in a plasmonic cavity, in good agreement with theoretical predictions. Such a giant suppression of photobleaching is well beyond conventional chemical schemes. Our findings will not only accelerate single-molecule fluorescence applications, but also open up a new avenue to electromagnetic control of chemical reactions.

      8:00 PM - CC6.24

      Plasmonic Bandgap Nanowire Nanocavities

      Jae-Hyuck  Choi1, Hong-Gyu  Park1, Soon-Hong  Kwon2.

      Show Abstract

      Plasmonic nanocavities enable significant light confinement in a subwavelength-scale volume. Although many plasmonic structures were fabricated through the deposition or patterning of metal films, the top-down approaches can cause high loss because deposited polycrystalline metal films introduce undesirable defects of scattering centers. In order to address these issues, we propose new plasmonic nanocavity that consists of silver nanowire and dielectric plasmonic bandgap structures. A chemically synthesized silver nanowire with single crystalline, defect-free surface is placed on a patterned dielectric substrate. Surface-plasmon-polaritons (SPPs) are then excited at the interface of nanowire/substrate. Numerical simulation shows that plasmonic bandgap can be opened in the silver nanowire on a high-index dielectric substrate with grating structure, and the bandgap frequency is determined by the grating periodicity. In addition, by missing a few gratings in the bottom dielectric substrate, a plasmonic nanocavity to confine SPPs in a desired region can be formed. To find an optimal design of the nanocavity, we changed several structural parameters such as cavity lengths, widths, and depths of air grating slots. We also investigated the dependence of nanowire cross-sections on the optical properties. The simulation results showed that Q factors of plasmonic modes excited by a nanowire with a square cross-section are higher than those of plasmonic modes by a nanowire with circular ones. To further enhance the confinement of plasmonic mode, thin air gap between silver nanowire and substrate can be introduced only in the cavity region. Hybrid plasmonic modes are then excited in a nanocavity with an air gap of 5 nm, and can show increased Q factors. We believe that this promising and novel plasmonic nanocavity developed using bottom-up synthesized silver nanowire will be useful for an ultimate light source in an ultracompact integrated circuit.

      8:00 PM - CC6.25

      Power Generation in Plasmonic Nanorectennas

      Richard  M.  Osgood1, Stephen  Giardini1, Joel  Carlson1, Megan  Hoey1, Gustavo  Fernandes2, Jimmy  Xu2, Jin Ho  Kim2, Prakash  Periasamy3, Ryan  O'Hayre3, Mathew  Chin4, Madan  Dubey4, Barbara  Nichols4, Philip  Parilla3.

      Show Abstract

      We generate power by illuminating arrays of plasmonic nanoantennas, consisting of electron beam-patterned Ag crossbar lines with “teeth” 70 - 300 nm long lying atop and parallel to ultrathin (less than 20 nm) tunneling barriers (NiO and NbOx (native)/Nb2O5). These oxide barrier layers, sandwiched between the Ag antennas and bottom metal (Nb or Ni) ground plane, form metal-insulator-metal (MIM) diodes [1,2]. These MIM diodes can be extremely fast, if their capacitance is low enough that the electron tunneling transit time dominates the response time, and their thickness is less than ~ 20 nm. The tunneling barriers rectify alternating currents, generated in the top metal layer by the incident visible/near-infrared (vis/nir) laser beams. When illuminated with a 532 nm nanosecond laser beam (pulse width ~ 10 nsec, peak power density 4*10^6 W/cm^2), both the nanorectenna arrays and the tunneling diodes themselves produce a small amount of power (~ 1 mV open circuit voltage, 20 uA short circuit current for Pt-Nb2O5-NbOx(native)/Nb diodes) [3]. Illuminating Ag-Nb2O5-Nb diodes with a continuous wave visible laser beam (wavelength 475 - 585 nm, power density 80 W/cm^2) produces an alternating voltage that tracks the diode’s current-voltage characteristic, consistent with rectification of the THz voltages generated across the MIM diode, although the signals are larger than what is predicted by classical rectification theory and our quantum mechanical mode of MIM diode conduction [4]. We measure the enhancement of these effects in the presence of the plasmonic Ag nanoantenna array with broad visible and narrower near-infrared resonances. In order to better understand the power conversion efficiency, we vary the diode material, top metal, laser beam angle of incidence, wavelength, power, and polarization. We interpret our results in terms of nanorectenna rectification, and/or other effects like unequal heating of carriers on either side of junction, photon-assisted tunneling, etc. [1] P. Periasamy, et. al., Adv. Materials 23 (2011) 3080. [2] M. L. Hoey, et. al., Appl. Phys. Letts. 97 (2010) 153104. [3] R. M. Osgood III, et. al., Proc. SPIE 8096, 809610 (2011). [4] R. M. Osgood III, submitted to J. Appl. Phys. (2012).

      8:00 PM - CC6.26

      Surface-assisted Laser Desorption/Ionization Mass Spectrometry Using Gold Nanorods on ITO Plates

      Masanori  Fujii1, Yasuro  Niidome1 2, Naotoshi  Nakashima1 2 3.

      Show Abstract

      Gold nanorods were fixed on an ITO plate and used for the spectroscopic sensing and Surface-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (SALDI-MS) of oligopeptides (angiotensin I). The longitudinal surface plasmon bands of the gold nanorods responded to the 10 fM angiotensin solution that was cast on the ITO plate. The SALDI-MS measurements had an ultra-high sensitivity to the angiotensin on the ITO plate. A very small surface density (5 × 10-19 mol/cm2) of angiotensin could be detected at m/z = 1297 with a good signal/noise ratio (S/N = 11). The ITO plate, which was modified with gold nanorods, was found to be effective in collecting angiotensin molecules adjacent to the gold nanorods, and the SALDI processes that were induced by the photoabsorption of the gold nanorods efficiently contributed the desorption and ionization of the angiotensin.

      8:00 PM - CC6.27

      YSZ Encapsulated Au Nanoparticle Films for Stable and Sensitive High Temperature Plasmonic Gas Sensing

      Gnanaprakash  Dharmalingam1, Nicholas  A  Joy1, Michael  Carpenter1.

      Show Abstract

      Nanocomposite films of Yttria stabilized Zirconia (YSZ) encapsulated Au nanoparticles have been fabricated by Physical Vapor Deposition (PVD). Extremely stable and repeatable sensing results of these films when exposed to gases such as CO and H2 at high temperatures (500°C) in an air carrier gas make them potential candidates for applications such as emissions monitoring and fuel cells. Well defined Au nanoparticles were formed by depositing and annealing a thin Au film on a YSZ surface. A thin capping layer of YSZ was then deposited to stabilize the Au nanoparticles at high temperature. A sensing response from the optical excitation of surface plasmons on the gold nanoparticles can be brought about by a change in the dielectric constant of the surrounding medium or from a change in the free electron density of Au nanoparticles, both of which can be affected by the oxidizing or reducing nature of the analyte gases. With YSZ playing the crucial role of a high-temperature oxygen ion conductor, films with varying thickness of the YSZ capping layer have been investigated for differences in the sensitivity and response time. Results from sensing tests will be shown, and future directions as to the selective sensing of gases among CO, NO2 and H2 will be discussed. Selective sensing could be achieved by either employing materials such as Pd, for example, which is sensitive to hydrogen, by changing the film composition or a combination of both. Prospective methods of achieving a single selective and sensitive nanocomposite film will also be presented and described.

      8:00 PM - CC6.28

      Enhanced Photostability of Chlorophyll-A Using Gold Nanoparticles as Efficient Photoprotector

      Laurent  Bekale1, Said  Barazzouk1, Prashant  V  Kamat2, Surat  Hotchandani1.

      Show Abstract

      Improving the photostability of chlorophylls is one of the main challenges to facilitate their industrial and biotechnological use. In this regard, we have employed gold nanoparticles (AuNPs) to photoprotect chlorophyll-a (Chla). Light absorption by Chla results in the formation of its excited singlets (1Chla*). If not readily used photochemically, they get converted into triplet excited states (3Chla*). Chlorophyll triplet states are long-lived energetic species which can easily react with the triplet ground state of oxygen (3O2) to produce strongly photooxidative reactive oxygen species (ROS). These ROS attack the nitrogens of the porphyrin macrocycle of Chla and cause its photodegradation. Therefore, if these nitrogen sites could be shielded from the attack of ROS by some harmless agent, Chla will be well protected. In the present work, we have demonstrated that AuNPs can greatly increase the photostability of Chla. The UV-Visible, fluorescence and X-ray photoelectron spectroscopic studies have been carried out to assess the effect of AuNPs on the photostability of Chla. The results show that with an appropriate concentration of AuNPs, as much as 80% photoprotection can be provided to Chla in solution. It is further seen that under in-vitro conditions, AuNPs are much better photoprotective agents of Chla than conventional protective agents, i.e., β-carotene or quinones, which are known to be very effective in natural living conditions (plants). The protecting ability of Chla by AuNPs is the result of their efficient binding with Chla at its nitrogen sites in dark, thus, inhibiting the reaction of ROS with Chla. The same property of AuNPs, i.e., to bind with Chla in dark, renders them better photoprotectant than carotene or quinones. The use of gold nanoparticles as efficient photoprotector of Chla, thus, offers us new possibilities to increase the photostability of various porphyrins used in a wide range of industrial (optoelectonic devices such as OLEDs and photovoltaics) and medical (photodynamic therapy) applications.

      8:00 PM - CC6.29

      Comparison of Plasmonic and Dielectric Nanostructures for Broadband Enhancement in Thin Film GaAs Photovoltaics

      Ragip  A  Pala1, Dennis  Callahan1, Kelsey  Whitesell1, Pierpaolo  Spinelli2, Albert  Polman2, Harry  Atwater1.

      Show Abstract

      It has been recently shown that statistical ray optical light trapping theory does not transfer to the ultrathin film solar cell regime and optically resonant metallic and dielectric structures can be used to enable significant absorption enhancements that can potentially exceed the 4n^2 statistical ray optics limit. Here we compare and contrast dielectric and plasmonic nanostructures for their potential to minimize surface reflectance and increase broadband light trapping for thin films of GaAs, the material used in record efficiency (n = 28.8%) single-absorber photovoltaic cells. To understand absorption enhancement mechanisms of dielectric and plasmonic nanostructures, we investigated 100 nm - 1 um GaAs thin films on both silica and metal substrates with periodic arrays of surface-applied silicon nitride and Ag nanostructures. We find that the active layer thickness determines the dominant enhancement mechanism: i) for ultra-thin (100 - 200 nm) films, plasmonic and dielectric Mie resonances that couple into waveguide modes are most significant enhancement mechanism; ii) for thicker films (500 nm - 1 um) both particle resonances and film thickness-related Fabry-Perot resonances determine cell performance. Using optimized structures, we obtain a 5-20% increase in the 1 Sun AM 1.5G photocurrent for 100 nm - 1 um thick GaAs cells, relative to the best conventional dielectric two-layer antireflection coatings. We find that plasmonic structures offer a large absorption enhancement for ultra-thin films while they provide limited access to resonance-driven light trapping for thicker films due to destructive Fano interference at the front interface. Dielectric structures on the other hand can be engineered to act as efficient light-trapping Mie scatterers and can serve as a broadband AR coating for both thin and thick films. To experimentally verify our predictions, we fabricated thin-film GaAs cells using epitaxial lift-off techniques. Nanoscale light trapping surface structures were fabricated using electron beam lithography, soft conformal nanoimprint lithography, and PECVD growth techniques. Results of GaAs cell spectral response measurements will be discussed and compared with model predictions.

      8:00 PM - CC6.30

      Fabrication of Structural Colored Mono-dispersed Spherical Assemblies and These Structural Color by Using Microflow Device

      Midori  Teshima1, Ryuji  Kawano2, Shinya  Yoshioka3, Syoji  Takeuchi4, Yukikazu  Takeoka1, Takahiro  Seki1.

      Show Abstract

      We unconsciously have had a damaging effect on environment with producing a variety of coloring materials for the development of humankind. As a result we had serious environmental problems caused by pollutions. Considering the rise of an environmental awareness, we need to produce environmentally friendly color materials. Structural colored materials must be the strong candidates because a variety of colored materials can be prepared just by changing the microstructures of the materials. Here, we describe the preparation of new structural colored materials by mixing white particles (SiO2) and black particles (Fe3O4) using a microflow system. Structural colors are caused by interference of light, scattering, and diffraction effects, and the color tint are influenced by refractive index and structural form of substances. [1]One of the most widely anticipated structural colored materials is a colloidal crystal film with a periodic optical nanostructure, composed of mono-dispersed submicron sized particles. Spherical assemblies (SAs) of the mono-dispersed colloidal particles are particular interest because of the possibilities for dispersed structural colored materials. In addition, such color materials can have the application potential for the biosensor. To use the SAs for such application, we need to obtain mono-dispersed SAs. To this end, we apply micro flow focusing device (MFFD) for preparing the mono-dispersed SAs of colloidal particles. We prepared MFFD made of poly(methyl methacrylate), which has a flow focusing geometry integrated into a planar flow channel of 300 mm diameter to form aqueous liquid drops containing particles in a continuous and immiscible oil phase (Span 80 surfactant is dissolved in hexadecane at 0.2 wt%). After drying the aqueous liquid drops in the oil phase by the application of heat, mono-dispersed SAs of silica particles were obtained. The size of the SAs can be controlled by changing the concentration of particles in the aqueous solutions. We made a series of the SA revealing different colorations with or without adding the magnetite particle (Fe3O4) and phenyl methyl ammonium chloride working as a salt. The hexagonal sharp peaks in the power spectra obtained by two-dimensional (2D) fast Fourier transforms (FFTs) of the scanning electron microscopy (SEM) images for the surface and inside structures of the brilliant colored SAs confirm the presence of short and long-range order. On the other hand, symmetrical and circular patterns around origin in 2D FFTs of SEM images for both structures of matte colored SAs confirm the presence of short-range order. The reflection spectra from these SAs also indicate these optical properties. In conclusion, we easily obtained a variety types of the spherical structural colored pigments composed of white and black particles by using of MFFD. References 1. Takeoka, Y. Angew. Chem. Int. Ed., 50, 4012-4015

      8:00 PM - CC6.31

      Silver Nanowires and Metal Grids for Transparent Conductors: Characterization and Modeling of Electrical and Optical Properties

      Garo  Khanarian1, Jake  Joo2, Xiang-Qian  Liu1, Dan  Werner1, Peter  Eastman1, Kathleen  O'Connell2, Peter  Trefonas2.

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      Silver nanowires are attractive as an alternative to ITO transparent conductors because of their high optical transmission and low sheet resistance. However, nanostructures inherently scatter light in comparison to thin continuous films, and this haze feature can be useful or detrimental depending on the application. In this paper, we will present a semi-empirical model that describes the nanowire dimension-property relationship. The model was developed based on the Mie theory of light scattering and percolation theory of random resistive 2D networks. Transparent conductor films were made with roll to roll continuous coating and spin coating using nanowires with various diameters and lengths. Based on the experiments and model, we will discuss the effect of diameter and length on scattering haze, and the critical exponents for sheet resistance near the percolation threshold. We will also present an optical and electrical model for micron size wide metallic periodic grids as transparent conductors. These results for random nanowires and periodic grids will be compared with literature values of other transparent conductors including ITO, CNT, PEDOT, and graphene.

      Download Session Locator (.pdf)2012-11-28  

      Symposium CC

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      Symposium Organizers

      • Matthew Doty, University of Delaware
      • Srikanth Singamaneni, Washington University
      • Andrey L. Rogach, City University of Hong Kong
      • Mark Brongersma, Stanford University
      • Vladimir V. Tsukruk, Georgia Institute of Technology

        CC7: Plasmonic Nanomaterials I

        • Chair: Peter Nordlander
        • Wednesday AM, November 28, 2012
        • Hynes, Level 2, Room 208
         

        8:30 AM - *CC7.01

        Quantum Plasmonics and Applications in Light Harvesting

        Peter  Nordlander1.

        Show Abstract

        A recently developed fully quantum mechanical approach for the description of plasmonic and excitonic nanoparticles and their interactions is presented. Quantum effects can have a pronounced influence on the electric field enhancements near the nanoparticle surfaces and on the optical properties strongly coupled nanoparticles.[1] For closely spaced metallic nanoparticles, electron transfer and nonlocal screening can drastically reduce the electric field enhancements across the gap and result in a Charge Transfer Plasmon (CTP) where an oscillatory electric tunneling current flows between the particles,[2] and strongly nonlinear effects can be induced.[3] The energy of the CTP is found to depend strongly on the electronic structure of the junction and the presence of molecules inside the gap.[4] For the coupled plasmonic-excitonic system where hybrid plexciton states are formed,[5] quantum effects can strongly modify the optical spectrum and a induce highly nonlinear optical response. The last part of the talk will be devoted to a discussion of plasmon decay into hot electron-hole pairs that can induce chemical reactions on the surface of the nanostructure [6] or be harvested directly in photodetector or photovoltaic geometries.[7] References [1] J. Zuloaga et al., Nano Lett. 9(2009)887; ACS Nano 4(2010)5269. [2] O. Perez-Gonzalez et al., Nano Lett. 10(2010)3090; R. Esteban et al., Nat. Comm. 3(2012)825. [3] C. Marinica et al., Nano Lett. 12( 2012)1333. [4] P. Song et al., J. Chem. Phys. 134(2011)074701; TBP. [5] A. Manjavacas et al., Nano Lett. 11(2011)2318; ACS Nano 6(2012)1724. [6] R. Huschka et al., J. Am. Chem. Soc. 133(2011)12247; S. Mukherjee et al., (2012)TBP. [7] M. W. Knight et al., Science 332(2011)702; Z.Y. Fang et al., Nano Lett. 12(2012)nl301774e.

        9:00 AM - *CC7.02

        Self-assembled Nanostructures for Linear and Nonlinear Response

        Augustine  Urbas1.

        Show Abstract

        Abstract- Metamaterials in optical frequencies have a tremendous range of application, many of which require large area materials with fine features. Self assembly can provide an efficient route to fabricating structured optical metamaterials. From enabling fundamentally new effects, such as optical magnetism, to creating tailored absorption and transmission spectra, designing optical properties through structure offers a new mechanism for manipulating light. These systems require nanometric features on structures frequently below 100nm in size in order to gain the desired properties set. To date, demonstrations have relied on electron beam lithography, focused ion beam milling and other high resolution techniques with limited ability to cover larger areas. This has limited experimental exploration of large area application of metamaterials. Self assembled systems can be used either directly as metamateials or as templating structures to create ordered arrays of meta-atoms. In addition, these techniques can be applied at the unit cell level to create complex, structured and active metamaterials. In this presentation, I will describe efforts to utilize self assembly techniques to create optical metamaterials. Systems designed to control fluorescence, nonlinear properties and optical absorption will be discussed.

        9:30 AM - CC7.03

        Light-management in Ultra-thin Conjugated Polymer Films on Metallic Ground Planes Using Vertically-oriented Nanoantennas

        Binxing  Yu1, Sarah  Goodman1, Alexa  Abdelaziz2, Deirdre  M  O'Carroll2 1 3.

        Show Abstract

        Nanophotonics, encompassing areas such as plasmonics, metamaterials and functional photonic materials, has emerged as a rapidly expanding new field for materials and device research in the past few years. As a result, important advances in fields such as photovoltaics, nano-optical sensors, enhanced information storage, light-emitting devices and photocatalysis have benefitted from a deeper understanding and improved control of light-matter interactions on the nanoscale. In particular, optical nanoantennas are capable of concentrating and enhancing optical fields to the nanometer-scale and receiving and transmitting optical signals in a highly directional way. Monopole nanoantennas, which consist of quarter-wavelength-long vertically oriented metal rods placed on a conductive ground plane, are of great interest due to their ease of fabrication and large signal directivity and gain. Here, we present how gold monopole nanoantenna arrays can be designed to affect the enhancement and localization of optical frequency electric fields in underlying semiconducting conjugated polymer (poly(3-hexylthiophene), P3HT) thin films. We fabricate a gold nanorod/P3HT/silver film monopole nanoantenna array system where the silver film acts as the conductive ground plane. The average height of the gold nanorod evaporated on P3HT was ~120 nm, whereas the P3HT layer thickness ranged from 10 nm to 70 nm (by controlling the concentration of P3HT in chloroform). Significant absorption enhancement up to 6 times in polythiophene is obtained using this system which is also validated by agreement with full-field electromagnetic simulation data. Under longitudinally polarized excitation, light is strongly localized both at the tip of the gold nanorod and in the underlying P3HT thin film. However, light is only localized on the surface of the gold nanoantenna under transverse polarization. We also suggests that there is an image plane effect between the gold nanorod and the underlying metal ground plane which causes the system to behave like a dipole antenna with large field intensity enhancement in the P3HT “gap” region. When light is polarized longitudinally, this strong gap mode intensity between the nanorod and the ground plane creates significant absorption-edge enhancement in polythiophene. Additionally, we show that longitudinal modes of the nanoantenna system can be tuned to enhance stokes-shifted, in-plane polythiophene emission by controlling the nanorod aspect ratio.

        9:45 AM - CC7.04

        Plasmonic Resonances in Self-assembled Reduced Symmetry Gold Nanorod Nanosystems

        Sushmita  Biswas1, Jinsong  Duan1, Dhriti  Nepal1, Ruth  Pachter1, Richard  Vaia1.

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        Plasmonic metamaterials have emerged as an area of significant interest due to their potential applications in the broad areas of photonics ranging from ultra sensitive chemical and bio-sensing, nanolasing and spectroscopy to photovoltaics and photodetection. Radiative losses are inherent in plasmonic systems and lower the quality factor (Q) of a resonance, where high Q resonance is desirable for higher near-field enhancement and stronger light matter interactions. Approaches to reduce these losses include structure design for exciting sub-radiant dark modes, reduced surface roughness and Fano resonances. Sub-radiant dark modes are beneficial due to their small line-width, high Q and reduced radiative damping; however they only couple weakly to the incident light due to their near-zero dipole moment. Symmetry breaking allows the manifestation of the dark modes, where the Dolmen structure is one of the simplest architectures (side by side pair of nanorods capped by a third nanorod). In this presentation we present a unique method of fabricating reduced symmetry Dolmen structures from the assembly of single and dimer pairs of chemically synthesized, single crystal gold nanorods. By changing the relative orientation of the cap nanorod with the dimer, we show that the hybridized local surface plasmon modes can be tuned to provide a factor of three higher electric field enhancements. A spectrally broad mode similar to a super-radiant mode is observed depending on the relative orientation of the structure to the incident excitation. These self-assembled colloidal plasmonic structures will be of significant interest for the fundamental study in plasmon coupling and light matter interactions facilitating the design of nanoplasmonic devices.

        10:00 AM -

        Break

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        10:30 AM - CC7.05

        Electrically Tunable Graphene-metal Plasmonic Antennas

        Yu  Yao1, Nanfang  Yu1, Patrice  Genevet1, Mikhail  Kats1, Federico  Capasso1.

        Show Abstract

        Dynamically tunable plasmonic structures have many potential applications, such as modulators, tunable SERS substrates, dynamic beam shapers, etc. Among the various tuning techniques, electrical tuning is generally more favored due to its high speed, simplicity and low-cost. Recently, graphene plasmonics has gained attention due to its electrically tunable optical properties. We designed and demonstrated metallic antenna structures on gated single layer graphene to investigate the feasibility of tuning antenna resonance via changing the gate voltage. Finite-difference time-domain (FDTD) simulation was used to design the structure and understand the coupling between the metallic antenna resonance and graphene plasmonic modes. We used commercial CVD (chemical vapor deposition) graphene transferred onto a SiOx substrate. Gold antenna arrays were patterned onto graphene surface using electron beam lithography. Reflection spectra were taken at various gate voltages using a Fourier transform infrared spectrometer (FTIR) equipped with a mid-infrared microscope. The tuning range of the antenna resonance is ~ 470 nm at ~7.3 µm (~87 cm-1, 5% of central operating frequency), which fits well with the FDTD simulation using the derived scattering lifetime (5e-14s). The tuning rate is ~0.12 nm/ (kV/cm). Moreover, simulations indicate that the tuning rate can be increased twice using graphene with 5 times longer carrier lifetime. Further experiment and calculation will be carried out with high quality graphene to achieve a broader tuning range.

        10:45 AM - CC7.06

        Coupling of Plasmon Modes in Nano-crescent Dimer Structures Fabricated by Colloidal Lithography

        Nicolas  Vogel1, Clemens  K  Weiss2, Katharina  Landfester2, Janina  Fischer2, Hans-Joerg  Butt2, Reza  Mohammadi2, Maximilian  Kreiter2.

        Show Abstract

        This contribution presents the construction and optical characterization of crescent shaped nanostructure dimers. Crescent shaped nanoparticles possess several interesting features. First, they support multiple, polarization dependent plasmon resonances in the near-infrared region. Second, strong near-field enhancements that are highly localized at the tip regions appear at the resonance wavelengths. Finally, they can be considered as nanoscale split ring resonators and are thus of interest for the design of metamaterials. The crescent structures can be conveniently produced by colloidal lithography in a cheap and fast process, either as sparsely distributed, separated objects[1] or in highly symmetric arrays by using a non-close packed monolayer as mask.[2] Here, we present two distinct approaches for the controlled placement of a second crescent in close proximity of a first one that lead to stacked[3]- or opposing[4] dimer architectures, respectively. The stacked double crescents are essentially quasi-three dimensional objects that can be vertically aligned with high precision. The latter architecture features two crescents that are aligned in the substrate plane with their tips facing each other. This dimer unit combines sharp tips with a small separation gap and thus possesses high near-field enhancements that are focused in an addressable hot-spot in between the tips. The close proximity of the two individual resonators leads to coupling of their individual plasmon resonances with drastic shifts of the resonance positions. We present a plasmon hybridization model[5] to explain the coupling behavior of the crescent dimers by simple geometric arguments for all polarization dependent resonances. Computer simulations were performed in order to support the established model. The near-field enhancements for the different structures at the resonance wavelength were accessed as well by computer simulations. [1] J. S. Shumaker-Parry, H. Rochholz, M. Kreiter, Adv. Mater. 2005, 17, 2131. [2] M. Retsch, M. Tamm, N. Bocchio, N. Horn, R. Forch, U. Jonas, M. Kreiter, Small 2009, 5, 2105-2110. [3] N. Vogel, J. Fischer, R. Mohammadi, M. Retsch, H. J. Butt, K. Landfester, C. K. Weiss, M. Kreiter, Nano Lett. 2011, 11, 446-454. [4] J. Fischer, N. Vogel, R. Mohammadi, H.J. Butt, K. Landfester, C.K. Weiss, M. Kreiter, Nanoscale 2011, 3, 4788 [5] E. Prodan, C. Radloff, N. Halas, P. Nordlander, Science 2003, 302, 419

        11:00 AM - CC7.07

        STEM EELs Characterization of Sub-10 nm Gaps between Crossed Silver Nanowire Waveguides

        David  T  Schoen1, Mark  L  Brongersma1.

        Show Abstract

        Recently there has been a growing interest in the resonant properties of metal nanoparticle dimers separated by extremely small gaps near and even below 1 nanometer. Here we examine the properties of small gaps not between metal nanoparticles, but metal nanowires. Chemically synthesized metal nanowires (NWs) are interesting and important plasmonic materials because they offer the ability to fabricate IMI structures with low intrinsic material losses whose effective index can be easily tuned by the NW diameter. Such waveguides have themselves have been the subject of numerous studies, and have shown promise as optical interconnects for small plasmonic circuits. We here fabricate a variety of silver NW crossbar structures separated by an Al2O3 dielectric spacer. The thickness of this spacer, and hence the spacing between the crossing NWs, can be controlled with Å precision using atomic layer deposition. We characterize the optical influence of these tiny gaps on the adjoining NW waveguides using plasmon mode mapping by Electron Energy-Loss Spectroscopy (EELS) in a Scanning Transmission Electron Microscope (STEM). By analyzing LDOS variations along the NW waveguides due to single surface plasmon polariton (SPP) reflections from the junctions, we can extract a variety of interesting values including the SPP dispersion relationship as well as the phase accumulation on reflection. Ultimately we believe these tiny junctions may provide an interesting route to tuning, and perhaps controlling, the resonant properties of the adjoining SPP waveguide segments.

        11:15 AM - CC7.08

        Wide Bandgap Semiconductors Supporting a Tunable Surface Plasmon Resonance in the Mid-IR

        Edward  Sachet1, Joshua  Guske2, Stefan  Franzen2, Jon-Paul  Maria1.

        Show Abstract

        Surface Plasmon Resonance (SPR) is a well-established sensing technique that commonly uses visible light in combination with thin metal films to sense minute changes in refractive index of the sensing surface. Using the visible spectrum requires an external light source and external optics thus limiting possibilities for a compact monolithically integrated system. Recently, we demonstrated SPR in transparent conductive metal oxides such as tin-doped indium oxide using near-IR light for excitation. However, shifting the SPR response to even lower frequencies will open exciting new possibilities for system integration. Mid-IR (4000-400 cm^−1) is a particularly interesting range since many mainstream semiconductors such as Si, Ge and GaAs are transparent to these energies. Integrating a solid-state mid-IR light source within a device structure containing a mid-IR SPR layer, could ultimately lead to fully integrated SPR based technologies. We demonstrate SPR in the mid-IR on two wide bandgap semiconducting materials, CdO and ZnO. For both material systems, heteroepitaxial thin films have been prepared on c-plane sapphire using pulsed laser deposition (PLD). The SPR was characterized in the Kretschmann-Raether configuration using a spectroscopic ellipsometer and a custom built stage. The data was compiled into angle and wavenumber dependent maps of the plasmonic response and will be compared to simulated maps based on a free electron Drude model adapted for the mid-IR. These simulations are in excellent agreement with the empirical data we present, thus offering a powerful tool in designing material systems and predicting their plasmonic response in the mid-IR. We further demonstrate that plasmon resonance in semiconductors enables active control of the surface plasmon properties. Due to the band gap in the plasmonic medium, light with super-bandgap energies can be used to actively change the carrier concentration in the conduction band, thus shifting the plasma frequency of the film and the resonance frequency of the surface plasmon. We will present mid-IR SPR data collected in situ to a second independent light source. In this case we used a UV Hg-arc lamp, which does not interfere with the SPR measurements due to the orders of magnitude difference in wavelengths. Light and dark SPR measurements for intrinsic ZnO and CdO films illustrate the ability to actively tune the surface plasmon. Comparison against simulations suggests that carrier densities are modulated by +1x10^18 cm-3 during illumination.

        -

        CC7.09 Transferred to CC13.04 on Friday

        Show Abstract

        11:30 AM - CC7.10

        Plasmonic Crystals with High Rotational Symmetry Fabricated by Moiré Nanolithography

        Steven  M.  Lubin1, Wei  Zhou2, Alex  J.  Hyrn2, Mark  D.  Huntington2, Teri  W.  Odom1 2.

        Show Abstract

        High rotational symmetry lattices are important in photonic and plasmonic applications because they interact uniformly with light independent of incident direction. We created a method to fabricate lattices over macroscale areas through moiré nanolithography with symmetries as high as 36-fold, three times higher than quasiperiodic lattices and six times higher than periodic lattices. We transferred these patterns into silver in order to create plasmonic crystals - ordered metallic structures that support the propagation of light as surface plasmon polaritons. Through angle-resolved reflectance spectroscopy, we observed that these structures formed considerably more plasmonic resonances in the visible spectrum than periodic arrays. Since the patterned area was much larger compared to other high-symmetry arrays, we were able to observe these plasmonic modes at high excitation angles. We indexed these resonances based on the locations of Bragg peaks, and determined the strength of the anti-crossing between plasmonic modes at degenerate energies and the same in-plane momentum. Because these arrays couple to visible light over a broad sprectrum, they can potentially increase the efficiencies of plasmonic-based photovoltaic devices.

        CC8: Coherent and Quantum Optics

        • Chair: Matthew Doty
        • Wednesday PM, November 28, 2012
        • Hynes, Level 2, Room 208
         

        1:30 PM - *CC8.01

        Cascaded Single-photon Emission and Coherence Properties of Mollow Triplet Sideband Emission from a Quantum Dot

        Peter  Michler1.

        Show Abstract

        Quantum information relies on the development of single, cascaded and entangled photon sources. For most of the applications Fourier transform-limited photons are an essential precondition. Therefore, the understanding and minimization of dephasing processes of quantum light emitters is a central issue in this research field. Resonance fluorescence emission from a single quantum dot has been proven to be nearly an ideal single-photon source for excitation powers below the saturation of the quantum dot [1, 2]. Here, we will present a detailed investigation of resonance emission above saturation of the quantum dot. In this regime the resonance spectrum develops into a triplet, the so called Mollow triplet. Two types of samples have been investigated, i.e. individual InGaAs/GaAs quantum dots embedded in planar waveguide structures and in high-quality pillar cavities. Both device structures have been optically addressed in an orthogonal geometry of excitation and detection which allows an effective collection of their resonance fluorescence signal while strongly suppressing parasitic laser stray light. Based on scanning Fabry-Pérot-type high-resolution photoluminescence series we could trace Mollow triplet spectra under variable excitation powers and detuning conditions. The spectral and statistical properties of the triplet strongly depend on pump power and detuning of the excitation laser. The photon correlation measurements demonstrate both ‘single’ and ‘cascaded’ photon emission from the Mollow triplet sidebands. The ultra-bright emission (4.7 MHz into the first lens) can be conveniently frequency-tuned by laser detuning over 15 times its linewidth [3]. Furthermore, the effect of dephasing in terms of systematic spectral broadening ~ Ω^2 of the Mollow sidebands and of oscillation damping in the photon coherence function g(1)(τ) are observed as a strong fingerprint of excitation-induced dephasing. Our results are in excellent agreement with predictions of a recently presented model on phonon-dressed QD Mollow triplet emission in the cavity QED regime [4]. References: [1] S. Ates, S.M. Ulrich, S. Reitzenstein, A. Löffler. A. Forchel, and P. Michler, “ Post-selected indistinguishable photons from the resonance fluorescence of a single quantum dot in a microcavity”, Phys. Rev. Lett. 103, 167402 (2009). [2] C. Matthiessen, A. N. Vamivakas, and M. Atatüre, “Subnatural linewidth single photons from a quantum dot”, Phys. Rev. Lett. 108, 093602 (2012). [3] A. Ulhaq, S. Weiler, S. M. Ulrich, R. Rossbach, M. Jetter and P. Michler, “Cascaded single-photon emission from the Mollow triplet sidebands of a quantum dot”, Nature Photonics 6, 238 (2012). [4] C. Roy and S. Hughes, Phys. Rev. Lett. “Phonon-dressed Mollow triplet in the regime of cavity quantum electrodynamics: excitation-induced dephasing and nonperturbative cavity feeding effects”, 106, 247403 (2011).

        2:00 PM - CC8.02

        Coherent Effects in Quantum Dot-metallic Nanoparticle Systems: Plasmonic Induction of Rabi Oscillation and Ultra-high Field Enhancement

        Seyed  M  Sadeghi1.

        Show Abstract

        Electric field enhancement caused by localized surface-plasmon resonances in metallic nanoparticles (MNPs) has been used for diverse applications, ranging from fundamental research in controlling optics of semiconductor quantum dots (SQDs) to the development of chemical and biological sensors. In many applications involving hybrid systems consisting of SQDs and MNPs, however, the plasmonic field experienced by the SQDs is mostly considered the prime property of the MNPs. In this contribution we theoretically show when such systems interact with a coherent light source (a laser field), quantum coherence in the SQDs can dramatically influence the plasmonic field of the MNPs. Therefore, the SQDs can self-renormalize the fields that they experience. In particular, we discuss when a SQD-MNP system interacts with an applied laser field with a step-like amplitude rise; the effective field of the SQD can exhibit a strong coherent oscillation, reaching significantly high values for short periods of time. We also show when the rise time of the applied field is such that the SQD by itself cannot exhibit Rabi oscillation, when it is in the vicinity of the MNP it can. These results suggest that in a SQD-MNP system quantum coherence not only changes the magnitude of the field that the SQD experiences, but also it can change the way this field changes with time. Therefore, compared to the applied field, the effective field can be delayed and its time variations can become much faster than those of the applied field. We study the resonance fluorescence of such systems, revealing how the effective fields influence ac-Stark shift and Mollow spectrum.

        2:15 PM - CC8.03

        Excitonic Properties of Visible Spectrum Quantum Light Single Photon Sources from InGaN/GaN Quantum Dots

        Stanko  Tomic1, Joydeep  Pal2, Max  Migliorato2, Robert  Young4, Nenad  Vukmirovic3.

        Show Abstract

        Sources of triggered entangled photons emitted from the biexcitonic cascade decay are highly desired for applications in quantum-cryptography and quantum- information processing, and were already realized in InAs/GaAs quantum dot (QD) material systems [1]. Radiative recombination from exciton (X) and biexciton (XX) states, confined in InGaN/GaN wurtzite QD, could potentially provide useful sources of visible quantum-light, targeting applications in the nascent field of quantum information, amongst others. To assess their potential, a theoretical methodology with which to calculate single-particle states was established, based on both an 8-band and 12-band strain-dependent envelope function k.p Hamiltonian, with contributions from the spin-orbit interaction, crystal-field splitting, piezoelectric and spontaneous polarization all included. Excitonic states were found using the configuration interaction method [2], whilst taking into account the important second-order effect of piezoelectricity in this III-N material system [3]. We compared the results of the 8-band k.p Hamiltonian with the artificially high C6v symmetry to the newly developed 12-band k.p Hamiltonian that predicts the correct atomistic C3v symmetry of the wurtzite QDs. The influence of mirror changes to the periodic boundary conditions were eliminated with a Makov-Payne correction, adapted to hexagonal and trigonal lattices. The optimal QD morphology for use in quantum light sources was determined by varying the diameter/height ratio (D/h), based on the optimization of the target function, which depends on the biexcitonic shift and optical dipole matrix element of the excitonic transition. The model established in this work is validated against experimental results on existing single GaN QD sources [4]. Further to this the model predicts that, with suitable variation of the In concentration within the QD, from 20 to 70%, it is possible to find morphologies that emit throughout the entire visible spectrum, i.e., from ~3 to 1.6 eV. Within this range of In-concentrations conditions can be found for the formation bound biexcitons. The competition between strong confinement in InGaN QDs and the internal electric field, generally reported in wurtzite III-N, was also investigated, as well as its effect on existence of bound biexcitons and a vanishing fine-structure spitting. The latter is a prerequisite for the on-demand generation of the entangled-photon pairs from InGaN-QD’s. [1] R. M. Stevenson, R. J. Young, P. Atkinson, K. Cooper, D. A. Ritchie, and A. J. Shields, Nature (London) 439, 179 (2006) [2] S. Tomic and N. Vukmirovic, Phys. Rev. B 79, 245330 (2009) [3] J. Pal, G. Tse, V. Haxha, M. A. Migliorato, and S. Tomic, Phys. Rev. B 84, 085211 (2011) [4]S. Kako, C. Santori, K. Hoshino at al, Nature Materials 5, 887 (2006)

        2:30 PM - CC8.04

        Two-color Antibunching from Band-gap Engineered Colloidal Semiconductor Nanocrystals

        Dan  Oron1, Zvicka  Deutsch1, Osip  Schwartz1, Ron  Tenne1, Ronit  Popovitz-Biro2.

        Show Abstract

        Quantum emitters of light usually tend to exhibit ‘photon antibunching’, emitting photons one by one, rather than in bursts. This implies nonclassical photon statistics, unlike those observed for classical sources such as lamps and lasers [1]. Antibunching, first observed in atomic systems, has since been observed from dye molecules, quantum dots and color centers. As light emission is usually observed only from the lowest excited state (‘Kasha’s rule’), it is essentially a two-level, single-color phenomenon. Here we devise a fluorophore which, upon photoexcitation, emits stochastically in either one of two distinct colors, but exhibits strong antibunching between them [2]. It is based on a multi-component colloidal quantum dot fluorophore having an engineered energy landscape and tailored exciton-exciton coupling. Our modular design opens a path for fabrication of new quantum light sources with significantly more complex emission properties, and can serve as a solid-state platform for nonlinear interactions, such as incoherent photon upconversion. [1] B. Lounis, M. Orrit, Rep. Prog. Phys. 68, 1129 (2005). [2] Z. Deutsch, O. Schwartz, R. Tenne. R. Popovitz-Biro, D. Oron, Nano Lett. Articles ASAP, DOI: 10.1021/nl300638t (2012).

        2:45 PM - CC8.05

        Exploring the Photoluminescence Spectral Lineshapes of Single Nanocrystals in Solution Using Photon-correlation Fourier Spectroscopy

        Jian  Cui1, Andrew  P.  Beyler1, Liam  Cleary1, Lisa  F.  Marshall1, Ou  Chen1, Hee-Sun  Han1, Daniel  K.  Harris1, Darcy  D.  Wanger1, Xavier  Brokmann1, Jianshu  Cao1, Moungi  G.  Bawendi1.

        Show Abstract

        Photoluminescence spectroscopy of single colloidal quantum dot nanocrystals (NCs) is particularly adept at revealing complex spectral properties typically hidden in inhomogeneously broadened ensemble-averaged measurements. However, conventional single-NC methods suffer from low temporal resolution, small sample size, and selection bias, and are susceptible to the broadening effects of spectral diffusion. Photon-correlation Fourier spectroscopy performed in solution (Solution PCFS) offers a novel approach to investigating the spectra of single NCs by sampling particles diffusing in solution with large sample statistics, without selection bias, and at timescales fast enough to avoid the spectral diffusion commonly observed in single-nanocrystal spectroscopy. Solution PCFS reveals that, for a given ensemble of particles with a known room-temperature spectrum, the average single nanocrystal possesses an a priori unknown spectrum that can differ greatly in shape and width, even among particles of the same core material composition. Our exploration of the dependence of the spectral linewidth on nanocrystal structural parameters reveals that the single-NC linewidth is weakly dependent on the core material composition. This indicates that the synthesis of InP or InAs core/shell particles with ensemble spectral linewidths as narrow as CdSe particles is limited by synthetic methodologies rather than any intrinsic material properties. Furthermore, we demonstrate for the first time that the single-nanocrystal linewidth can be synthetically tuned over a wide range of widths. Using a simple lineshape model, we explore the physical origin of this spectral diffusion-free single-NC spectral lineshape and assess the changes in exciton-phonon coupling in relation to nanocrystal structural parameters.

        3:00 PM -

        Break

        Show Abstract

        3:30 PM - *CC8.06

        Spins and Photons of Quantum Dots

        Mete  Atature1.

        Show Abstract

        Self-assembled semiconductor quantum dots are interesting and rich physical systems. Their inherently mesoscopic nature leads to a multitude of interesting interaction mechanisms of confined spins with the solid state environment of spins, charges and phonons. In parallel, the relatively clean spin-dependent optical transitions make quantum dots strong candidates for stationary and flying qubits within the context of spin-based quantum information science. I will discuss current progress in coherent generation of single photons suitable (and tailored) for linear-optics quantum computation and for establishing a high-efficiency spin-photon quantum interface within a distributed quantum network.

        4:00 PM - *CC8.07

        Universal Quantum Control of Quantum Dot Spin Qubits in a Cavity

        Sophia  Economou1.

        Show Abstract

        The spin of a confined carrier (electron or hole) in a quantum dot has many desirable properties for quantum computing applications: it can be controlled with fast optical pulses and coupled to other spins via photonic cavities and waveguides, while it is also an excellent single photon emitter. High finesse coherent control is necessary to implement the quantum logic gates necessary to carry out quantum computation, including single-qubit and entangling two-qubit control. I will present our recent theoretical work on coherent control of spins. In particular, I will focus on the design of a deterministic entangling gate mediated by a common cavity mode coupled to two spin qubits. Our gate is explicitly compatible with single-spin rotations, and along with these forms a universal set of gates for quantum computing. We calculate the fidelity as a function of the cavity Q and the spontaneous emission rate of the quantum dot, providing a guide to experiment. I will demonstrate how our design can accommodate several qubits for a single cavity mode, thus opening the road to a scalable architecture with quantum dot spin qubits.

        4:30 PM - CC8.08

        Optical Isolation Based on Electromagnetically-induced Transparency

        Mehmet Cengiz  Onbasli1, Juejun  Hu2, Lei  Bi1 3, Taichi  Goto1, Caroline  Ross1.

        Show Abstract

        The ability to allow light propagation in only one-way enables the design of functional devices such as optical isolators (i.e. diodes for light), optical circulators, magneto-optical switches, modulators, sensors, magneto-optical antireflection coatings for solar cells and windows and opens up previously unavailable and unexplored physics of nonreciprocal photonics. The viability and implementation of nonreciprocal photonics has been enabled by magneto-optical materials, active modulation of optical constants, and nonlinear optical response of materials. The fabrication of magneto-optical materials such as cerium-doped yttrium iron garnet (Ce1Y2Fe5O12) on silicon-based photonic substrates enables the implementation of integrated nonreciprocal photonic devices such as an isolator based on a ring resonator [Bi et al., Nat. Photonics 5 758 2011]. Previous designs of such nonreciprocal photonic devices have focused on the demonstration of materials integration on the silicon-based chip. In this study, we merge magneto-optical functionality with electromagnetically induced transparency (EIT) and demonstrate in simulation an increase in the bandwidth of magneto-optical isolators by two orders of magnitude to at least 100 GHz (<500 MHz without EIT). We start with a model waveguide system in which a waveguide is coupled to two ring resonators with same radii, but different losses (i.e. 100 and 0.1 dB/cm). Then, we excite the waveguide system with a waveguide mode and the propagating light excites the resonators. Because of the large difference between the optical losses of the resonators, photon lifetime in the first resonator is much shorter than in the latter. When light has decayed in the first resonator, optical power in the second resonator is still live and this provides the control signal of EIT. When the waveguide is now excited with the signal, the control signal in the second ring prevents coupling from the waveguide to the first ring within a band of the resonance of the resonators. As a result, a non-negligible range of wavelengths has been prevented from coupling to the rings within the resonance band, leading to a W-shaped transmission spectrum for the waveguide system. This provides the on-chip photonic construct of EIT. By depositing a magneto-optical thin film on one of the resonators, we break time-reversal and space-inversion symmetries. As a result, the resonance wavelengths for forward and backward propagating light are no longer degenerate. In addition, EIT forms asymmetric resonance peaks for the resonators. Our simulations indicate bandwidth and isolation ratio improvements can further be enhanced.

        4:45 PM - CC8.09

        Reversible Light-induced on-off Switching of Charge Traps in Quantum Dots Probed by Variable-pulse-rate Photoluminescence Spectroscopy

        Mauro  Aresti1, Marco  Marceddu2, Michele  Saba1, Francesco  Quochi1, Jing  Huang3, Dmitri  V.  Talapin3, Andrea  Mura1, Giovanni  Bongiovanni1.

        Show Abstract

        Colloidal semiconductor nanocrystals can be the material of good choice for a wide variety of optical applications owing to their tuneable optical gaps and their easy processability. Nanocrystals can be used as light absorbers and emitters in optoelectronic devices such as light-emitting diodes, photodetectors and solar cells. Furthermore, colloidal quantum dots represent a remarkable alternative to organic fluorophores in a wide range of life science applications as they exhibit good photostability, large absorption cross-sections and narrow emission lines. Charge carrier trapping at the nanocrystal surface is a key phenomenon because it reduces the quantum efficiency of light emission. Surface passivation through passivating ligands can remove trap states yielding enhanced photoluminescence quantum yields. However, capping molecules are not covalently anchored to the surface. The local configuration of surface atoms and ligands can undergoes slow changes caused by the stochastic interaction with the environment. Surface instabilities have been recently conjectured as a possible origin- alternative to the presence of free charges- of the blinking behavior of the emission intensity of nanocrystals under continuous wave illumination. It has been also speculated that configurational changes of the nanocrystal surface could be triggered by light. Experimental evidences of these mechanisms are, however, fragmentary. We devise an experiment to control and probe both the activation of nonradiative trapping centres and charge accumulation with a variable-pulse-rate laser source. We apply variable-pulse-rate photoluminescence spectroscopy to study CdS/CdSe core/shell nanocrystals in diluted solutions and close-packed thin films. We find that nonradiative traps are reversibly activated by light, i.e., nanocrystals return bright below a pulse fluence threshold. Photocharging are reversibly induced in nanocrystal solutions, but showed a memory effect in films, decreasing significantly after prolonged illumination.

        CC9: Poster Session: Optical Materials and Devices III

        • Wednesday PM, November 28, 2012
        • Hynes, Level 2, Hall D
         

        8:00 PM - CC9.01

        Metallic Thin Films with Tunable Optical Properties

        Krishna  Muralidharan1, Slimane  Laref1, Keith  Runge1, Pierre  A  Deymier1, Richard  W  Ziolkowski2, Jiangrong  Cao3, Mamoru  Miyawaki3.

        Show Abstract

        The development of devices with the ability to display dynamically tunable optical properties over a relatively broadband in the visible spectrum is a worthy technological challenge for new image sensor functions and requires materials that are capable of exhibiting ‘on-demand’ dielectric properties. Towards this end, using first-principles density functional theory (DFT) based approaches in conjunction with a less-rigorous Jellium models, we characterize the size-dependent and external electric field-dependent optical properties of nanometric gold thin films in the size-range 5-50 nm. The results clearly indicate that the plasmonic and optical properties of such thin-films can be significantly controlled by external stimuli. Using these results as the basis, we also demonstrate that the optical transmission/reflection properties of nanometric gold thin film-based metamaterials can be significantly tuned. These tunable metamaterials hold great promise for applications in tunable plasmonic and optical components and devices.

        8:00 PM - CC9.03

        Fluorescence Resonance Energy Transfer between Tri (8-hydroxyquinoline) Aluminium/Oligonucleotide Nanorod and Fluorescent Dye

        Chunzhi  Cui1, Jinsoo  Joo2, Dong June  Ahn1.

        Show Abstract

        We fabricated hexagonal shape tri (8-hydroxyquinoline) aluminium (Alq3)/oligonucleotide nanorods with a facile re-precipitation method. The shape of nanorods also shown hexagonal type as the 3’ end of oligonucleotide labeled with Cy3 or Cy5 fluorescent dye. A significant fluorescence resonance energy transfer (FRET) was observed at isolated Alq3/ oligonucleotide nanorod which the 3’ end of oligonucleotide labeled with Cy3 fluorescent dye due to emission of Alq3 nanorod and absorption of Cy3 fluorescent dye have the spectral overlap. However, as the 3’ end of oligonucleotide labeled with Cy5 fluorescent dye, there was no FRET observed due to emission of Alq3 nanorod and absorption of Cy5 fluorescent dye have small spectral overlap.

        8:00 PM - CC9.05

        Pulsed UV Laser Annealing for Subsurface Modification of Nanoparticles towards Local Surface Plasmon Resonance Engineering in AlN:Ag Thin Films

        Demosthenes  Koutsogeorgis1, Anastasios  Siozios2, Elefterios  Lidorikis2, Wayne  Cranton1, Constantine  Kosmidis3, Panos  Patsalas2.

        Show Abstract

        We have recently reported the photosensitivity of Aluminium Nitride (AlN) films with embedded silver nanospheres [1]. AlN exhibits several high quality characteristics (transparent, inert, hard) and is one of the widely used materials in photonics. With the effective incorporation of Silver (Ag) nanoparticles we have been able to ascribe further characteristics, namely a Local Surface Plasmon Resonance (LSPR). In this work we have grown, by Pulsed Laser Deposition, AlN thin films incorporating Ag nanoparticles, and have subjected them to Pulsed UV Laser Annealing (LA) with two different wavelengths (KrF and ArF) at a varying number of pulses and fluence, in ambient conditions and in inert overpressure. LA of AlN:Ag thin films alters, not only the Ag inclusions’ size and shape distribution but also the refractive index of the surrounding matrix. The photosensitivity of AlN:Ag enabled the optical data storage and the encoding of optical information that is spectrally-sensitive, durable, and of high spatial resolution, in contrast to organic dyes and photoresists, whose general liability is that they are not durable in harsh environmental conditions. The spectral selectivity of micron-size patterns encoded in AlN:Ag plasmonic templates is evaluated by optical microscopy observations, using various single-color optical sources (lasers or LEDs) in the visible spectral range. We will present the spectral selectivity variations of patterns encoded with LA using the aforementioned different laser wavelengths (193 nm and 248 nm). In addition, the effect of the substrate's optical absorption is considered in detail. We will show that spectrally sensitive encoding can only be achieved by using the AlN:Ag plasmonic templates and not any other interference-colored AlN layers. The experimental optical data were analysed using the Maxwell-Garnett effective medium theory. Finally, we identify the structural changes that take place (using Scanning Electron Microscopy and X-Ray Diffraction). The results show that the LSPR signal is enhanced due to the subsurface enlargement of the existing Ag nanoparticles, whilst its spectral position is red-shifted due to the subsurface, again, modification of the AlN host locally surrounding the nanoparticles. Therefore we demonstrate that pulsed UV laser annealing, which is applicable at with very high spatial resolutions and to films grown onto temperature-sensitive substrates, can be used for the fabrication and modulation of subsurface structures inside functional dielectric hosts, with advanced photosensitive characteristics. [1] A. Siozios et al, Nano Lett. 12, 259 (2012).

        8:00 PM - CC9.07

        SERS on Geometrical-controlled Metal Nanodot Arrays Prepared Using Anodic Porous Alumina

        Toshiaki  Kondo1, Kazuyuki  Nishio1 2, Hideki  Masuda1 2.

        Show Abstract

        The fabrication of ordered arrays of noble metal nanoparticles has attracted attention because these nanostructures has a capability to enhance the electric filed of incident light based on localized surface plasmon resonance (LSPR).1,2 Optical functional devices composed of metal nanoparticle arrays, such as chemical and biological sensing devices, have been proposed. Precise control of the geometrical structures of the nanoparticle arrays is important because the properties of LSPR are substantially dependent on the shape and arrangement of the nanoparticles. There have been numerous reports on the preparation of an ordered nanostructure of metals for optimizing LSPR properties. However, processes for easy precise control of the structure of metal particles have not been established. In the present work, we examined the fabrication process of geometrical-controlled nanodots using anodic porous alumina as an evaporation mask, and its application to the substrate for the measurement of surface-enhanced Raman scattering (SERS). One of the advantageous points of using the anodic porous alumina to fabricate nanostructures is that the shape and arrangement of the obtained nanostructures can be controlled by changing the geometrical structures of the porous alumina. The anodic porous alumina membrane was obtained by anodization of Al in acidic solution followed by wet-etching processes. Au was deposited onto the substrate through the nanoholes of the alumina mask by thermal evaporation method. After removing alumina membrane, Au nanodot arrays were obtained on the substrate. Raman scattering spectra were measured using a Raman microscope equipped with a He-Ne laser (wavelength: 633 nm). The obtained structure was dipped in a pyridine solution and dried in air before the measurement. The Raman peaks originating from the adsorbed pyridine molecules were observed at 1014 and 1040 cm-1. The intensity was strongly dependent on the shape and arrangement of the nanodots. The present process allows the easier preparation of SERS substrates compared to the process employing the electron beam lithographic technique. The obtained SERS substrates will be used for the Raman spectra measurement with high sensitivity. [1] T. Kondo, F. Matsumoto, K. Nishio, H. Masuda, Chem. Lett., 37, 466 (2008). [2] T. Kondo, H. Miyazaki, K. Nishio, H. Masuda, J. Photochem. Photobiol. A, 221, 199 (2011).

        8:00 PM - CC9.08

        Large-Scale Synthesis of Gold Nanorods with Tailored Surface Plasmon Resonances

        Wei-Chen  Wu1, Krystian  A.  Kozek1, Klaudia  M.  Kozek1, Sumeet  R.  Mishra1, Joseph  B.  Tracy1.

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        Gold nanorods (GNRs) are of significant interest for their tunable longitudinal surface plasmon resonance (SPR), which depends on the nanorod aspect ratio. Potential applications of GNRs are often limited by the small scale of typical GNR syntheses. In order to maximize the yield, a secondary growth phase is performed, where reducing agent is continuously added while stirring, thereby driving the reduction of unreacted Au(III) to Au(0) and its deposition onto existing GNR seeds. Stirring is generally believed to reduce the yield of rod-shaped nanoparticles, but we show that the solution can be stirred during the secondary growth phase while preserving the nanorod shapes. Stirring while continuously adding the reducing agent has enabled the development of a simple method for synthesizing concentrated solutions of GNRs on the liter scale. Moreover, this method also enables the growth of different sizes of GNRs of the same aspect ratio, thereby enabling control of the ratio of scattering to absorption. GNRs with longitudinal SPR wavelengths that can be tuned between ~530-1000 nm have been synthesized by adjusting the amounts of the reactants.

        8:00 PM - CC9.09

        Tunable Fano Resonance in Symmetric Multilayered Gold Nanoshells

        Ovidio  Yordanis  Pena Rodriguez1, Antonio  Rivera1, Mariano  Campoy-Quiles2, Umapada  Pal3.

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        Fano resonances (FRs) are typical spectral features caused by the coupling of a discrete state with a continuum [1]. This phenomenon has been known for many years in atomic physics and constitutes the basis for the electromagnetically induced transparency (EIT) [2]; however, only recently it has been achieved in all-plasmonic systems [3]. In addition to fundamental scientific interests, plasmonic Fano resonances in strongly coupled systems give rise to the so-called plasmon-induced transparency (PIT) [4], a phenomenon similar to EIT. PIT, in turn, has a great potential for the fabrication of sub-wavelength waveguides, low-loss metamaterials and chemical sensors [5]. In this work we have studied the evolution of dipole-dipole all-plasmonic Fano resonances in symmetric multilayered nanoshells as a function of their geometrical parameters. We have demonstrated that symmetry breaking is not mandatory for controlling the Fano resonance in such multilayer structures. Carefully selecting the geometrical parameters, the position of FR can be tuned in between 600 and 950 nm and its intensity can be increased up to four folds with respect to the non-optimized structures. Generation of FRs in such symmetric nanostructures presents clear advantages over their asymmetric counterparts, considering their easier fabrication process and wider technological applications. 1. U. Fano, "Effects of configuration interaction on intensities and phase shifts," Phys. Rev. 124, 1866-1878 (1961). 2. K.-J. Boller, A. Imamolu, and S. E. Harris, "Observation of electromagnetically induced transparency," Phys. Rev. Lett. 66, 2593-2596 (1991). 3. G. Bachelier, I. Russier-Antoine, E. Benichou, C. Jonin, N. Del Fatti, F. Vallée, and P.-F. Brevet, "Fano profiles induced by near-field coupling in heterogeneous dimers of gold and silver nanoparticles," Phys. Rev. Lett. 101, 197401 (2008). 4. S. Zhang, D. A. Genov, Y. Wang, M. Liu, and X. Zhang, "Plasmon-induced transparency in metamaterials," Phys. Rev. Lett. 101, 047401 (2008). 5. N. Liu, T. Weiss, M. Mesch, L. Langguth, U. Eigenthaler, M. Hirscher, C. Sönnichsen, and H. Giessen, "Planar metamaterial analogue of electromagnetically induced transparency for plasmonic sensing," Nano Lett. 10, 1103-1107 (2010).

        8:00 PM - CC9.10

        Observation of Magnetic-field-induced Scattering via Far-field Measurements

        Matthew  Moocarme1, Benjamin  Edelstein1, Luis  Dominguez1, Alexa  Lempel1, Luat  Vuong1.

        Show Abstract

        Plasmon control in nanoparticles via frequency modulation or external magnetic field provides a means to manipulate a materials properties as well as its nanoscopic structure. Plasmon control of nanocolloid solutions has applications in bottom-up metamaterial synthesis and active plasmonics. Here, we measure an increase in the scattering in gold nanocolloid solution when DC and slowly oscillating magnetic fields, aligned with the direction of incident light, is applied. Laser and non-laser lamps are used as light sources, and the polarization is varied between linear and circular. We show that magnetic field intensities on the order of mT result in changes of up to 6.5 percent in far-field scattering. Transient changes in the nanocolloid absorption and scattering efficiency, and spectra are observed in the far-field interference patterns. Additionally, when an appreciable external magnetic field is applied, the resulting changes are sustained after the magnetic field is switched off. Sample memory of the applied magnetic field is impressive as the nanocolloid solution is highly disperse (0.25mg/mL) [1]. We explain our experimental observations as the result of selectively excited surface plasmon polariton (SPP) modes in gold nanospheres[1,2]. Magnetic properties [1,3] that are coupled to the surface plasmon resonance (SPR) of the gold nanospheres result in material anisotropy via existence of electrical surface current loops. A rotating electric field vector, can also excite SPR modes, driving solenoidal currents via Drude model, generating a magnetic media[4], which has also been explored. Subsequently, control of the nanocolloid scattering via appropriate adjustment of either the external magnetic field or incident frequency modulation is attainable. From experimental data we have found that this results in an additional magnetic field dependent refractive index term that acts linear as a function of intensity. From our experiments and analysis, we deduce that an additional magnetic field dependent term is required on the effective refractive index of the nanocolloid solution. This enables additional plasmon control through the use of magnetic fields. The transient responses of the absorption and scattered spectra from oscillating external magnetic fields present interesting application for plasmon based optical filters. References: 1. Singh, N.D. et al, "Anomalously-large photo-induced magnetic response of disperse metallic nanocolloids in aqueous solution using a solar simulator", (submitted). 2. Drezet,A. et al, "Surface Plasmon interference Fringes in Back Reflection", EPL, 74(4), 2006. 3. Michael,F. et al, "Size Dependence of Ferromagnetism in Gold Nanoparticles: Mean Field Results" Physical Review B, 76(22), 2007. 4. Hertel,R., "Theory of Inverse Faraday Effect in Metals", J. Magn. Magn. Med., 303(L1-l4) 2006.

        8:00 PM - CC9.11

        Opto-electronic Properties of Chemically Exfoliated 2D Layered Transitions Metal Dichalcogenides

        Damien  Adrien  Voiry1, Hisato  Yamaguchi1, Takeshi  Fujita2 4, Mingwei  Chen2, Goki  Eda3 5, Manish  Chhowalla1.

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        The isolation of 0D (macromolecular cages), quasi 1D (nanotubes and nanowires) and 2D materials has demonstrated that properties of such materials are determined not only by the interatomic chemical bonding but also by their dimensionality. For example, 2D MoS2 is a direct band gap semiconductor that exhibits photoluminescence while the bulk material is an indirect band gap semiconductor. We have recently demonstrated using a previously reported method that highly concentrated aqueous solution of single layer MoS2 can be obtained through lithium intercalation [1]. We have extended this method to several other (WS2, MoSe2, WSe2) semiconducting layered transition metal dichalcogenides (LTMDs). Our analysis of the exfoliated samples reveals that lithium intercalation induces a reversible phase transition due to displacement of the chalcogen atoms. As a consequence, the solution-processed thin films of the as-exfoliated LTMDs were found to be metallic. The metallic behavior progressively disappears upon mild annealing and semiconducting structure can be restored as confirmed by PL signals in single layer thin films. [1] Eda, G. et al. Nano Lett. 11, 5111-5116 (2011).

        8:00 PM - CC9.12

        Linear and Nonlinear Photoluminescence from Planar Arrays of Au Nanoparticles

        Gary  Walsh1 2, Luca  Dal Negro1.

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        It has been proposed that light emission from metal nanoparticles could be used as a highly efficient sensor to refractive index variations. In this work, we design planar arrays of Au nanoparticles fabricated by electron beam lithography on silica substrates and demonstrate the tunablity of their photoluminescence (PL) spectra by systematically varying the particles size and separation. By comparing PL spectra with dark field scattering we show that the localized surface plasmon (LSP) resonances supported by theses structures significantly alter the emission line shape from that of bulk Au. The PL peak wavelength is found to occur blue shifted from that of the dark field scattering however, we demonstrate a one to one linear correlation between these peak positions as they scale with particle size. Furthermore, we show that PL excited by two photon absorption (2PA) with a 785 nm, 120 fs Ti:Sapphire laser displays an additional intensity dependence on the particles size not observed in linear emission. Using numerical modeling we show that these effects arise from the resonant excitation of LSPs resulting in near-field enhancement that increases the excitation efficiency of 2PA. These studies are important for the engineering of nonlinear plasmonic devices for communication and sensing applications.

        8:00 PM - CC9.13

        Photoemission Enhancement caused by Tunable Surface Plasmon Excitation Wavelength of Gold Caps on InGaAs Quantum Disk Array

        Jian  Huang1, Hongwei  Gao1, Jun  Lu1, Ning  Xiang1, Aaron  James  Danner1, Jinghua  Teng2.

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        We report the photoemission enhancement of an AlGaAs quantum disk array covered with gold caps by a surface plasmon resonance generated around gold particles. An orthogonal two dimensional (2-D) periodic nanostructure array of gold caps was designed on an underlying quantum disk array of AlGaAs, a widely used optoelectronic material. To do this, a 2-D nanoarray of gold particles was fabricated via interference holography with a certain designed period above an AlGaAs quantum well layer with an emission wavelength of 770nm. A chemical solution etch was then used to make AlGaAs quantum nanodisks under the gold mask caps. Different depths and widths of quantum nanodisks were studied by varying the etching time. A tunable shift of spectral response in absorption was observed, attributed to the surface plasmon resonance and was also a function of etching time. A factor of 2.5 enhancement in light emission was observed when the optical response wavelength was close to the wavelength of the quantum disks, unlike the situation when the two wavelengths were mismatched. FDTD simulation showed agreement with the tunable shift and contributes to explaining this shift which is caused by the surface plasmon excitation around the gold particles. The photoemission of AlGaAs quantum disks was thus enhanced due to the occurrence of coupling between the surface plasmon resonance wavelength and the quantum disk’s emission wavelength. The results provide a convenient method of tuning a surface plasmon resonance wavelength to coupling with different quantum disks’ wavelength and exciting its photoemission. Acknowledgments This work is supported by the Singapore Ministry of Education Academic Research Fund under grant: MOE2009-T2-1-086.

        8:00 PM - CC9.14

        Gold Nanoparticles Supported on SrTiO3 by Solution Plasma Sputter Deposition for Enhancing UV-and Visible-light Photocatalytic Efficiency

        Gasidit  Panomsuwan1, Nobuyuki  Zettsu1 3, Nagahiro  Saito1 2 3.

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        The growth of industry has enormously increased the generation of waste by-products, leading to a serious environmental problem. Metal oxides (e.g. TiO2, SrTiO3, ZnO, etc.) have been extensively used for pesticide degradation and water splitting under UV irradiation. However, due to the relatively low solar radiation intensity in UV region (<4%), shift of the responsive band gap energy toward visible region is highly desirable. To approach this requirement, metal oxides supported gold nanoparticles (AuNPs) are rapidly gaining interest in recent catalyst research because the AuNPs can act as a source for promoting interfacial charge separation processes. Thus, the interfacial bonding between AuNPs and metal oxide surface is a critical factor for effective photocatalytic properties. In the present study, we purpose a novel method for fabricating SrTiO3 (STO) supported AuNPs. The AuNPs were rapidly synthesized and directly deposited onto the STO surface in one-step by solution plasma-based sputtering of Au electrode. Solution plasma, non-equilibrium plasma in solutions, provides us considerable advantages in the field of nanoparticles such as clean products, narrow size distribution, open system under atmospheric pressure, and rapid synthesis. Results obtained from a high-resolution transmission electron microscope showed that well-crystallized AuNPs with an average size of 5 nm and narrow size distribution were observed on the STO surface. Absorption spectra showed a surface plasmon resonance band centered at 560 nm, indicating the presence of AuNPs. For the photocatalytic measurement, degradation of the dye under UV irradiation was investigated to be enhanced for AuNPs-STO in comparison with pure STO. The influence of AuNPs loading and particle size on the photocatalytic efficiency in UV and visible regions were also investigated and discussed. The solution plasma sputter deposition is expected to have a potential for fabricating metal oxide supported metal nanoparticles for photocatalytic applications in the future.

        8:00 PM - CC9.15

        Scalable Generation of Structured Particles through an In-fiber Fluid Instability

        Joshua  Kaufman1, Guangming  Tao1, Soroush  Shabahang1, Hooman  Banaei1, Daosheng  Deng2, Xiangdong  Liang3, Steven  Johnson3, Yoel  Fink4, Ayman  Abouraddy1.

        Show Abstract

        Applications ranging from drug delivery to cosmetics require generating microparticles and nanoparticles from different materials and with various structures. Here we present a new method for the fabrication of spherical particles utilizing the scalability of fiber fabrication technology and an in-fiber Plateau-Rayleigh capillary instability (PRI). By thermally treating multi-material fibers after drawing, spherical particles of many sizes and various structures are generated. Common methods for fabricating such particles are hindered either by a narrow choice of materials, particle structure, or particle diameter. By utilizing the PRI in multi-material fibers, we have fabricated particles ranging in size from 20 nm to 1 mm. Furthermore, by employing a stack-and-draw process, many fibers may be embedded into subsequent preforms and drawn, resulting in a single cladding matrix containing a high density of cylindrical core materials to increase the particle production rate that is comparable or better than most other methods. The robust nature of PRI is illustrated through the fabrication of more complex structures such as core-shell, Janus, and even multi-sectioned “beach ball” particles. The materials chosen for these fibers need only be thermally matched such that they may be drawn together. If the particles need to be released from that cladding matrix, then a suitable solvent should be found such that it can dissolve the cladding material and leave the particles untouched. In our work, we have so far focused on a polyethersulfone (PES) cladding and a chalcogenide glass core. The core size determines the resulting particle diameter, so specific sizes can be achieved by simply fabricating a fiber that has a core diameter that will yield the desired particle size. This also applies to the fibers with a high density of cores. All cores break up simultaneously and at the same size, to within 10% of the targeted particle diameter. More complex structures are obtained by strategically designing the preform. Core-shell particles are obtained from a fiber with a polymer core surrounded by a glass layer. When the core is comprised of two half cylinders each of a different glass material, the result is a Janus particle, a bi-compartmental particle that is half of each material. We predict that even more complex structures may be generated as well as particles from other materials, such as polymers, liquids, metals, and semiconductors.

        8:00 PM - CC9.17

        Silver Nanoclusters in Lithium Niobate

        Steffen  Milz1, Jura  Rensberg1, Carsten  Ronning1, Werner  Wesch1.

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        Embedded metal nanoclusters are of special interest in optical devices (such as optical filters, waveguides, etc.) due to their plasmonic properties. The advantage over surface nanoclusters is that they have defined and homogeneous surrounding with a constant dielectric function leading to a well-defined surface plasmon resonance (SPR). In the present contribution, we have synthesized silver nanocluster embedded in lithium niobate, which is the most important material for integrated optics due to its unique electro-optical and nonlinear optical properties. The synthesis was achieved by silver ion implantation and the implantation as well as annealing parameters gives us very good control on the cluster size distribution. The irradiation induced crystal damage was investigated by means of RBS, TEM and XRD. In addition, polarization depended optical spectroscopy was used to measure the position of the SPR for both ordinary and extraordinary polarized light for all cluster size distributions. These results were in excellent agreement with respective simulations based on Mie’s theory. Here, one critical parameter is the crystal quality of the LiNbO3 matrix surrounding. We determined that higher implantation temperatures as well as post implantation annealing is suitable to achieve perfect recrystallization, which is a necessary premise for the use of such plasmonic metal nanocluster in lithium niobate optical devices.

        8:00 PM - CC9.18

        Plasmonic Halo: A Nanogap-excited Surface Plasmon Standing Wave Resonance

        Fan  Ye1, Michael  J.  Burns1, Michael  J.  Naughton1.

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        We have fabricated and modeled via electromagnetic simulations surface plasmon standing wave resonances that are excited by optically-illuminated metallic nanogaps. In microscale disks prepared with optically-plasmonic metals, visible light incident on a like metal surface separated from the disk by a nanogap can induce plasmon modes. The outer metal can then form a type of "halo" boundary condition that confines the propagating plasmon, yielding a standing wave pattern akin to a plasmonic corral. We have observed and characterized such standing wave patterns in the near-field using NSOM. In addition, we have observed novel far-field effects via optical microscopy, wherein changing the size(s) of the disks and/or nanogaps enables tuning of the wavelength of light launched into far-field from the plasmonic halo. This work is supported by the W.M. Keck Foundation.

        8:00 PM - CC9.20

        Plasmonic Effects in Hybrid Chromium-gold Nanostructures

        Ali  Nejat1, Seyed  M  Sadeghi1 2.

        Show Abstract

        Significant research is currently conducted towards applications of localized surface plasmon resonances for chemical and biological nanosensors, novel therapeutic methods, imaging, optical devices, drug delivery, etc. The on-going research also includes investigation of fundamental physics involving applications of near fields of metallic nanoparticles for manipulation of the optics of semiconductor quantum dots. In this contribution we report the results of our recent investigation of plasmonic effects in hybrid metallic nanostructures consisting of gold and chromium. These nanostructures were fabricated by forming gold nanoislands on glass substrates followed by sputtering of a layer of chromium on the top. We used such structures, which contained gold nanoparticles semi-covered and interconnected with chromium, as meta-substrates for deposition of a thin film of colloidal CdSe/ZnS quantum dots. We performed spectroscopic measurements to investigate the plasmonic peaks of such substrates and intensity and spectral changes of emission of the quantum dots while the thickness of the chromium layer was changed. Our results showed distinct plasmonic field enhancement features when the thickness of the chromium layer varied from 1 to 50 nm. This includes augmentation of plasmonic emission enhancement factor of the quantum dots compared to those on glass substrates covered by the same thickness of chromium (no gold metallic nanoparticles), as the thickness of the chromium layer was increased. We discuss the physics behind this and the impact of photo-oxidation of quantum dots by chromium oxide.

        8:00 PM - CC9.21

        Plasmonic Nanostructures from Single-crystalline Metallic Films

        Jong Hyuk  Park1 2, Palak  Ambwani2, Michael  Manno2, Nathan  Lindquist2, Prashant  Nagpal2, Sang-Hyun  Oh2, Chris  Leighton2, David  Norris1.

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        Precisely patterned nanostructures with low damping of surface plasmon polaritons (SPPs) are of critical importance in plasmonic applications. However, grain structure in conventional polycrystalline metallic films can decrease the quality of desired patterns due to induced roughness and increased SPP losses on the films. Herein, we report a simple approach to obtain precise nanostructures with improved dielectric properties based on single-crystalline metallic films. These films were prepared by epitaxial growth of silver on mica substrates at elevated temperatures. Under controlled deposition conditions, the films had extremely flat surfaces over large areas. The dielectric functions of the resulting films were compared with those of polycrystalline films with identical surface roughness. The dielectric functions of the single-crystalline films showed a larger negative real component and a smaller imaginary component, giving higher electrical conductivity and smaller optical absorption, respectively. These results indicate that the absence of grain boundaries significantly reduces Ohmic losses and scattering, leading to improved dielectric properties and increased propagation lengths for SPPs. Furthermore, when nanostructures were fabricated by focused-ion-beam milling, the uniform nature of the single-crystalline films allowed more precise patterning of high-quality nanostructures, while the different grain orientations in the polycrystalline films resulted in increased roughness within the patterned areas. The single-crystalline films can therefore provide an effective route to plasmonic devices with enhanced performance.

        8:00 PM - CC9.22

        Controlling Surface Plasmon Polaritons via the Solid to Liquid Phase Transitions in Gallium

        Clifford  J  Engel1, S. R. c.  Vivekchand1, Steven  Lubin1, Martin  Blaber1, George  Schatz1, Teri  Odom1 2.

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        In order to realize surface plasmon polariton (SPP)-based photonic devices, there is a need for external, on-demand control of plasmonic properties. Temperature-induced solid-to-liquid phase change allows for the direct manipulation of SPPs within a plasmonic material. We have fabricated 1D Ga gratings using a combination of photolithography, reactive ion etching, and nanomolding techniques. These substrates support plasmonic resonances at visible wavelengths, with a 3-fold increase in SPP coupling efficiency as solid Ga melts. The liquid phase also exhibited a narrower resonance, which suggests a longer SPP lifetime in the liquid phase compared to the solid phase. By taking advantage of the supercooling characteristics of Ga, we were able to lower the freezing point of Ga, and, as a result, control the temperature at which the phase transformation occurs.

        8:00 PM - CC9.23

        Platinum Optical Nano-antenna Fabricated by Electron Beam Induced Deposition

        Eun-khwang  Lee1, Jung-Hwan  Song1, Min-Kyo  Seo1.

        Show Abstract

        Electron beam induced deposition (EBID) has been a promising fabrication method that realizes rapid construction of nano-scale structures. With precursor gas nozzles installed in a scanning electron microscope (SEM), deposition at a predetermined position with a desired size is possible. Recently, the EBID method has been employed as a subsidiary tool for various applications, such as welding carbon nanotubes, tuning a photonic crystal resonator precisely and supporting a backbone for an extremely sharp atomic force microscope tip. However, there was little research precedent about optical characteristics of EBID-made nanostructures as a functional device. In this research, we demonstrated a platinum optical nano-antenna directly formed by the EBID method using the precursor gas, [(CH3)3(CH3C5H4)Pt]. Pt media can support surface plasmon polaritons (SPPs) for the full visible wavelength range without considerable interband transitions. Pt nano-rod antennas were deposited on a silica substrate along the x- or y-axis with magnification control from 50 K to 200 K for a desired length. The initial acceleration voltage was 30 kV with 100 μA emission current. During the three-minute-deposition, current was measured via a Faraday cup showing 60~80 pA. The length of the rod was controlled from 1 to 2 μm with a fixed width of ~150 nm. We measured the optical characteristics of the EBID Pt nano-rods and examined their properties as optical antennas based on polarization-resolved dark-field (DF) microscope. The Pt nano-rods generated antenna radiations strongly polarized along the rod axis even under unpolarized white light illumination. It is well-known that dielectric nano-rods support not only transverse electric (TE) but also transverse magnetic (TM) antenna modes simultaneously. Therefore, the strong linear polarization characteristics can be an indirect evidence of SPP currents propagating back and forth along the rod. This reciprocating motion can form a standing wave, leading to a multi-lobe radiation pattern. We observed the radiation pattern in the Fresnel region with a 532-nm and 660-nm lasers, and the number of spaced multi-lobes relied on the length of the Pt rod. Reaching a conclusion that our EBID antennas show plasmonic characteristics is still ongoing since they were not composed of 100 % pure Pt. Carbon is inevitably deposited due to organic materials within the SEM chamber. We verified the atomic percentage of a free-standing Pt wire using energy dispersive X-ray spectroscopy (EDX) and the Pt composition was close to approximately 32 % compared to carbon and oxygen after oxygen plasma ashing. We expect that the purity of Pt can be improved much further with various technics such as annealing, plasma treatment and so on.

        8:00 PM - CC9.24

        Fabrication of High-aspect Ratio Single Crystalline Gold Nanowires: Nanoscale Confinement Growth in TiO2 Nanotubes under UV Irradiation

        Seonhee  Lee1, Hyunjun  Yoo1, Hyunchul  Kim1, Myungjun  Kim1, Yunjeong  Yang1, Hyunjung  Shin1.

        Show Abstract

        One dimensional (1D) nanostructures of Au have attracted much attention due to their novel physical and chemical properties. There are few methods to synthesize 1D Au nanowires (NWs) with the control of diameter and length. Among them seed-mediated growth and electrochemical replication of nanoporous membranes are the most successful method for the fabrication of high-aspect ratio Au NWs. In case of the electrochemical replication can be produced Au NWs in high yield with high aspect ratio, but most of the NWs are polycrystalline. Seed-mediated method offers relatively large quantities of NWs with high crystalline quality. However the method produces not only NWs but also large fractions of nanoparticles or nanoplates. In this study, nanotubular structure of TiO2, which is widely used as photocatalyst, was used as a key material to synthesis high aspect ratio Au NWs, without adding any surfactant, reducing agents or metal nuclei as seeds. Crystalline anatase TiO2 nanotubes (NTs) were prepared by atomic layer deposition (ALD) with replications of anodic aluminum oxides (AAO) membranes (Bea et al. Chem. Mater. 2008, 20, 756; Bea et al. MRS Bull. 2011, 36, 887). After ALD process, TiO2 NTs was removed from AAO and dispersed on Si substrates, and then the substrates with the dispersed NTs were in the solution of HAuCl4 at the temperature of 5°C. High aspect ratio metallic Au NWs were synthesized under UV irradiation of the NTs. Maximum aspect ratio of ~ 500 single crystalline Au NWs with the length of 20 μm with the diameter of 40 nm were obtained by perfectly filling in TiO2 NTs. Often the fabricated Au NWs were multi-twinned, and the twin planes are formed in random fashion, for example, perpendicular or parallel to the longitudinal direction of Au NWs. The nucleation events are seemed to be quite random temporally as well as spatially. Electrons photo-excited on the surfaces of TiO2 NTs under the UV irradiation reduce Au ions and create nuclei. Photo-generated electrons were continuously provided from TiO2 and injected to Au nuclei simultaneously. Once the nucleation events occur, Au NWs grow rapidly as single crystalline with high aspect ratio. With the pH variations of the precursor solutions, at low pH value (~ 6), Au are nucleated and grow as NWs only inside of TiO2 NTs. The number of necessary OH- ions, which are assumed to be directly responsible for the reduction of Au ions, will increase locally only inside of TiO2 NTs. Nanoscale confinement in the TiO2 NTs leads to OH- ion production and subsequently the growth of Au NWs along the pores. Even though the growth mechanism of 1D Au NWs inside of TiO2 NTs is yet to be ascertained, it is apparent that the nucleation events and the subsequent growths in surrounding media are crucial to the formation of high aspect ratio metallic NWs. Measurements of surface plasmon polariton resonances of high aspect ratio single crystalline Au NWs by dark-field mode of optical microscopy will be presented.

        8:00 PM - CC9.25

        Spectroscopic Properties of Gold-silver Core-shell Nanorods on an ITO Plate

        Yukiko  Tsuru1, Yasuro  Niidome1 2, Naotoshi  Nakashima1 2 3.

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        Anisotropic metal nanoparticles have been attractive research targets, because they showed multiple SP bands in the visible and near infrared regions. Various anisotropic silver nanoparticles have been reported, and the anisotropic nanoparticles showed broad SP bands in the visible region because of multiple and overlapped SP bands. We have reported silver-shelled gold nanorod [1-4]. Our particles were uniform in shape, and the simple rod-shape produced four SP bands in the visible region. The origins of these bands have thus far been unclear. In this work, we obtained the extinction spectra of the SP bands by varying the incident angles of the monitor light. The core-shell nanorods were deposited on a glass and an ITO plates. SEM observations indicated that some of these nanorods were standing on an ITO plate. The extinction spectra of the plates were measured by varying the angles of incidence of p-polarized monitor light. Deconvolution of these spectra produced six bands in the visible region. The dependence of the peak intensities on the incident angles strongly indicated that the bands at 390 and 420 nm originated from surface plasmon bands in the transverse direction of the nanorods. Extinction spectra of the glass and the ITO plates for various incident angles of the monitor light were examined to investigate the peak intensities of the two peaks at around 390 and 420 nm depending on the incident light angles. In the cases of both the glass and the ITO plates, the peak intensities at 390 nm increased markedly with increasing incident angle. In contrast, the peak intensities at 420 nm gradually decreased with increasing incident angle. These profiles were consistent for the two plates. The increasing peaks at 390 nm are thought to have originated from an SP band for which the transition dipole moment was perpendicular to the plate surface. The increasing tilt angle increased the excitation probability of the transition that was perpendicular to the plate surface. Some nanorods are lying flat on the ITO plate, and these horizontal nanorods contributed the increasing peak intensities at 390 nm. The band at 420 nm probably comes from a SP oscillation in the transverse direction of the standing core-shell nanorods. On the ITO plate, some of nanorods were standing upright on the surface; this band was thus found to have a major peak at around 420 nm.

        8:00 PM - CC9.26

        Design of Aluminium Plasmonic Nano-antenna for Ultraviolet Light Confinement

        Chun-Ho  Lee1, Kwang-Yong  Jeong2, Jung-Hwan  Song1, Min-Kyo  Seo1.

        Show Abstract

        Plasmonic nano-antennas have gained considerable interest because of their ability to localize electromagnetic fields into a sub-wavelength region and modify far-field emission profile. Due to its large damping and interband transitions in the ultraviolet (UV) region 200 nm<λ<400 nm, novel metal such as Au and Ag is inadequate to excite a UV localized surface plasmon (LSP). On the other hand, Al with a weak interband activity can support the LSP in the UV region. Recently, the UV LSP resonance enhancements in the Al nano-antennas are being reported: an Al nano-aperture structure was used to enhance a fluorescence of amino acids and an enhanced Raman signal coupled with Al coated Si cantilever tip was observed. Especially, Liancheng Zhou et al. demonstrated a UV bowtie nano-antenna formed by the focused ion-beam (FIB) milling. However, such a small bowtie structure for a UV wavelength is not suitable to be fabricated easily and precisely by conventional electron beam lithography. In this study, We investigate an Al plasmonic antenna on a quartz substrate consisting of only two nano-disks for easy and precise fabrication. In order to study optical properties of the resonant mode of the antenna, we perform three-dimensional (3D) finite-difference time-domain (FDTD) simulation. The plasmonic antenna successfully confines the UV lights in a subwavelength region of about 30 x 30 x 30 nm^3, where the UV lights are injected from the quartz substrate. We expect that this confined region would be small enough to achieve local interaction between antenna resonance and a single quantum emitter such as a fluorescence dye and a semiconductor quantum dot. In the antenna with nano-disks with a diameter and thickness of 90 and 30 nm respectively, 32-fold field intensity enhancement at around the 30-nm-gap was achieved at a target wavelength of 370 nm. In particular, a extinction cross-section of ~0.069 μm^2 that is ~5.4 times larger than the structural cross-section of the antenna was achieved, where each disk has an area of 0.0064 μm^2. This indicates the effective interaction of the proposed antenna with the incident UV light. We also observed that the spectral behaviors of the resonance and the extinction cross-section can be controlled by changing the length of the disk diameter. On the other hand, the field enhancement dominantly depends on the gap size.

        8:00 PM - CC9.27

        Crystal-structure Dependent Growth of Bimetallic Nanostructures and Their Plasmonic Properties

        Qian  Li1, Ruibin  Jiang1, Jianfang  Wang1.

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        Metal nanocrystals with different sizes and shapes are of great interest because of their plasmonic, catalytic, and magnetic properties. They have been increasingly employed in diverse technological applications ranging from biochemical sensing and imaging to solar energy harvesting. Compared with monometallic nanocrystals, multi-component metal nanostructures can exhibit new plasmonic properties that are not possessed by their single-component counterparts. They can also introduce better catalytic properties than single-component ones, where one metal can enhance the stability and the others promote the catalytic performance. Moreover, multi-component metal nanostructures can bring about many new functions, such as nanobarcodes and magnetoplasmonic effects. Due to the high shape dependence of the physical and chemical properties, morphological control of multi-component metal nanostructures is crucial for obtaining desirable properties. Extensive efforts have been devoted to the understanding of the effects of surfactants, seeds, and redox potentials on the growth of multi-component metal nanostructures. On the other hand, it is also of vital importance to understand the nature of the rich plasmon modes in multi-component metal nanostructures, because different plasmon modes exhibit distinct optical properties, which in turn determine their plasmon-based applications. We have studied the growth behavior of silver and palladium on single-crystalline Au nanorods (SC Au NRs), multi-twinned Au nanorods (MT Au NRs), and multi-twinned Au nanobipyramids (MT Au NBPs). The growth conditions are kept the same for the same metal, except the amount of the metal precursor. Both silver and palladium exhibit a highly preferential growth on the side surfaces of the SC Au NRs, whereas they prefer to grow at the ends of the MT Au NRs and MT Au NBPs. These phenomena indicate that the prepared bimetallic nanostructure products are highly dependent on the crystal structures of the starting Au nanocrystal seeds. We have furthermore ascertained the evolution and nature of the four plasmon modes in the Au core-Ag shell nanostructures, which have a cuboidal shape. The four plasmon modes are found through systematic electromagnetic calculations to be the longitudinal dipolar mode, transverse dipolar mode, and two octupolar modes, respectively, in the order of decreasing plasmon resonance wavelengths. The observed dependence of growth behavior on the crystalline structure of the starting Au nanocrystal seeds will help in understanding the growth mechanism and thereafter paving the way for finely controlling the shape of multi-metallic nanostructures. Our understanding of the plasmonic properties of the Au core-Ag shell nanostructures will be useful for designing bimetallic nanostructures and utilizing their attractive and rich plasmonic properties for various applications, such as a variety of plasmon-enhanced spectroscopies.

        8:00 PM - CC9.28

        Position-dependent Plasmon Coupling in Gold Nanorod-nanosphere Heterodimers

        Caihong  Fang1, Lei  Shao1, Jianfang  Wang1.

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        The plasmon resonances of noble metal nanocrystals can couple together when the nanocrystals are placed in close proximities. Such coupling leads to spatial electromagnetic energy redistribution and changes in the light scattering and absorption spectra, which is essential for a number of plasmon-based technological applications. Extensive investigations have therefore been made on understanding and modulating the plasmon coupling between metal nanocrystals. Usually only dipole-dipole bonding plasmon modes are active under light excitation for homodimers that are composed of two identical metal nanocrystals due to their high symmetry in both the shape and material. Heterodimers formed by two metal nanocrystals with either different shapes or materials exhibit richer plasmon coupling behaviors owing to the symmetry breaking. The plasmon coupling behavior in metal nanocrystal heterodimers depends on the metal type, size distribution, and spatial arrangement of the two components. Up to now, nearly all of plasmonic heterodimers investigated are rotationally symmetric with respect to the interparticle axis, where the spatial symmetry is not completely broken. We have carried out investigations on the plasmon coupling in the heterodimers made of a large Au nanorod and a small Au nanosphere. The rotational symmetry of the system is broken when the nanosphere moves away from the end of the Au nanorod. The breaking of the rotational symmetry provides an additional freedom for controlling the plasmonic properties of the heterodimers. We find that the plasmon resonance of the nanorod is strongly modulated by the small Au nanosphere. Intriguingly, the nanosphere dipole rotates around the nanorod dipole to achieve favorable attractive interaction for the bonding dipole-dipole mode. The heterodimer exhibits Fano interference, with its spectral features being strongly dependent on the position of the nanosphere relative to the nanorod. We also find that the plasmon responses are sensitive to the gap distance and the size of the constituting monomers. The optical response varies with both the vertical and lateral displacements of the Au nanosphere. In particular, the optical responses are extremely sensitive to the position of the Au nanosphere when the gap distance is less than ~2 nm. Our Au nanorod-nanosphere heterodimers will therefore be able to function as an excellent plasmon ruler with two spatial variables for measuring the nanoscale distance changes in biology and nanoelectromechanical systems.

        8:00 PM - CC9.30

        Silver Nanoparticles Embedded in a PEDOT Film Prepared via Electrochemical Route: A Controllable Roughened Optically Active Nanomaterial

        Uzeyir  Dogan1, Murat  Kaya2, Atilla  Cihaner2, Murvet  Volkan1.

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        A simple, reliable and reproducible one-step electrochemical method for the preparation of surface-enhanced Raman-active polymer-mediated silver nanoparticles (AgNPs) on planar indium tin oxide (ITO) coated glass substrates was reported. Poly (3,4-ethylenedioxythiophene (PEDOT) film was used as a support material for dispersing nanostructured silver nanostructures on the surface homogeneously, since 3,4-ethylenedioxythiophene (EDOT) monomer polymerizes regioregulary. The optical properties and morphologies of the silver substrates have been investigated by ultraviolet-visible (UV-vis) spectroscopy and field emission scanning electron microscopy (FE-SEM). The UV-vis and FE-SEM results revealed that the Ag nanostructures separately appeared on the PEDOT coated ITO after reduction. The effect of the thickness of PEDOT polymer film, reduction potential of silver, the concentration of silver ion solution and the amount of silver particle on the polymer film on the optical property will be studied as well as repeatibilty and temporal stability of prepared materials.

        8:00 PM - CC9.31

        Altering the Dewetting Characteristics of Ultrathin Gold Films Using Sacrificial Layers

        Pouyan  Farzinpour1, Kyle  D  Gilroy1, Aarthi  Sundar1, Zachary  E  Eskin1, Robert  A  Hughes1, Svetlana  Neretina1.

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        Precious metal nanostructures immobilized on substrate surfaces are of importance to numerous potential applications in the areas of photovoltaics, catalysis, chemical and biological sensing, the formation of nanowires via the vapor-liquid-solid growth mode and as shadow masks for reactive ion etching. The early stage investigations in these emerging fields relied heavily on substrate-based nanostructures derived from the room temperature deposition of continuous ultrathin films onto substrates followed by their subsequent agglomeration at elevated temperatures. The widespread use of this thermal dewetting process, however, was largely reliant on the ease at which such nanostructures can be fabricated over large areas, typically produced in a few hours using simple instrumentation consisting of a room temperature sputter coater and a tube furnace. Apart from this simplicity aspect, the nanostructures produced were unsatisfactory from many standpoints as there exists a lack of control over the nanoparticle size distribution, spacing and placement on the substrate. We have studied the dewetting characteristics of ultrathin gold films when deposited, not on a bare substrate, but on a variety of sacrificial layers which either sublimate or evaporate during the agglomeration process. In numerous instances, it was observed that the sacrificial layer significantly enhances the areal extent over which the agglomeration occurs. Moreover, the enhancement observed is proportional to the thickness of the sacrificial layer deposited. It is demonstrated that, for a given gold thickness, the average gold particle size can be shifted from tens of nanometers to micrometer length-scales as the average nanoparticle spacing is increased and the gold plasmon resonance red-shifts. This is in stark contrast to the conventional dewetting approach where, for a given film-substrate combination, little can be done to substantially alter the dewetting characteristics. The application of this technique to other precious metals will also be discussed.

        8:00 PM - CC9.32

        Three-Dimensional Surface Diffusion: A New Route for Manipulating the Size Distribution and Placement of Supported Gold Micro- and Nano-structures

        Aarthi  Sundar1, Pouyan  Farzinpour1, Kyle  D.  Gilroy1, Chris  J.  Decker1, Robert  A.  Hughes1, Gabriel  A.  Devenyi2, John  S.  Preston2, Svetlana  Neretina1.

        Show Abstract

        Substrate-supported gold nanostructures have a wide-range of potential applications as enhancement agents in photovoltaics and light emitting diodes (LEDs), as catalytic seeds for nanowire growth and as sensing agents in biological and chemical detectors. While numerous routes exist for the fabrication of such structures, the dewetting of an ultrathin film at elevated temperatures stands out as one of the most economical routes to nanostructure formation over large areas. The process is contingent on the fact that the film is deposited on a substrate having a surface energy lower than that of gold. Upon heating, the surface diffusion of atoms causes the gold film to agglomerate into isolated islands having nanoscale dimensions. This dewetting process, although simple, is limited in its technical application due to a lack of control over size uniformity, spacing and particle size. In a new approach, we demonstrate that the dewetting process can be manipulated by placing the free surface of the gold film in contact with a metal foil as it dewets. By confining the agglomeration process in this manner the gold atoms have the freedom to move parallel to the substrate as well as in the third dimension onto the surface of the foil creating a 3-dimensional surface diffusion field. The surface energy gradient between the oxide and foil results in a net migration of gold atoms from the nanostructure to the foil. With time, the nanostructures show a size reduction and a narrowed size distribution. The narrowing results from the formation of foil contact points with only the largest nanostructures, a characteristic which leaves small nanostructures intact while consuming larger ones. Using the same technique, but where the metal foil is replaced with a nickel mesh, it is also possible to control the agglomeration process of thick gold films in a manner which yields periodic arrays of gold microstructures. This directed assembly approach combines elements of subtractive transfer patterning and templated dewetting. When heated, the gold beneath the mesh selectively attaches to it due to a surface energy gradient which drives gold from the low surface energy oxide surface to the high surface energy nickel mesh. With this process being confined to areas under and adjacent to the mesh, the underlying gold film eventually ruptures at well-defined locations to form isolated islands of gold which subsequently dewet. Removal of the mesh reveals a periodic array of highly-faceted three-dimensional gold microstructures.

        8:00 PM - CC9.33

        Distance-dependent Refractive Index Sensitivity of Gold Nanorods

        Limei  Tian1, Ramesh  Kattumenu1, Max  Fei1, Abdennour  Abbas1, Naveen  Gandra1, Srikanth  Singamaneni1.

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        Owing to the facile tunability of the localized surface plasmon resonance (LSPR) and large refractive index sensitivity, gold nanorods (AuNR) are of high interest as plasmonic nanotransducers for label-free biological sensing. We investigate the influence of gold nanorod dimensions on distance-dependent LSPR sensitivity and electromagnetic (EM) decay length using electrostatic layer-by-layer (LbL) assembly of polyelectrolytes. The electromagnetic decay length was found to increase linearly with both the nanorod length and diameter, although to variable degrees. The rate of EM decay length increase with nanorod length was significantly higher compared to that of the diameter. The ability to precisely measure the EM decay length of nanostructures enables the rational selection of plasmonic nanotransducer dimensions for the particular biosensing application.

        8:00 PM - CC9.34

        Convertible Polyaniline Nanoprobes for Recognition of Redox Potential

        Yoochan  Hong1 2, Jihye  Choi3, Eugene  Lee4, Yong-Min  Huh2 4 5, Seungjoo  Haam2 3, Dae Sung  Yoon1, Jaemoon  Yang2 4.

        Show Abstract

        In recent years, polyaniline (PANI) has been promising conducting polymer because of its ease of synthesis, environmental stability and unique doping/dedoping and oxidation/reduction mechanism. Because of these characteristics, in research area in electronic devices, PANI has been used to electrodes itself or coated film as electronic enhancer. One of the most unique characteristic of PANI is convertible optical property varying its doping/dedoping state. We confirm that optical absorbance peak of PANI is red-shifted toward the long wavelength, generally NIR region, as a result of its transition from the emeraldine base (EB) to the emeraldine salt (ES) during the doping process. Using this characteristic of PANI, thus, we study with PANI as photothermal agent to ablate A431 epithelial cancer cells. Interestingly, the PANI changed its color from green to blue, when it was treated to cancer cells. This indicates that state of PANI is transformed from EB to ES and absorbance peak of PANI is red-shifted toward the NIR region, consequently, ES PANI is well-suited as a photothermal agent for use with NIR laser irradiation at 808 nm, which does not damage blood or normal tissue. We next try to make stable and small size PANI nanoparticles in aqueous solution, so we synthesize water-soluble nanoparticles (TPANI) based on PANI using Tween80 as a surfactant via solvent-shifting method. The TPANI have better stability as well as smaller size in aqueous solution than our first approach. TPANI also show sensitive color transition that caused by its oxidation/reduction states. In addition, we examine the possibility of TPANI as indicators to determine the cancer cells redox status because cancer cells release the biological dopants that can be doped with PANI toward reduction state. We finally investigate the synthesis of targetable PANI nanoparticles (HAPANI) using hyaluronic acid for specific receptor, CD44 expressed on MDA-MB-231 breast cancer cells. In the case of HAPANI, the sensitive color changes varying doping/dedoping state of HAPANI are also exhibited, furthermore, specific targeting ability for CD44 receptor is shown as varying the cancer cell state (live or fixing) and cancer cell lines (MDA-MB-231 or MCF7, both of breast cancer cells). Moreover, various candidates of biological dopants can be doped with HAPANI such as metabolic acids and co-enzymes, etc. In summary, we synthesize nanoparticles based on PANI using various synthetic methods and apply PANI nanoparticles to various biological applications. First, synthesized PANI nanoparticles are used as a photothermal agent, we also confirm that PANI nanoparticles can be used as a nanoprobe for cancer cell status, and finally, we investigate targeting ability of PANI nanoparticles with specific targeting moiety, hyaluronic acid for specific receptor, CD44.

        8:00 PM - CC9.35

        [Ag44(SR)30]4-: A Silver-thiolate Superatom Complex with Long-lived Charge-separated States

        Yun  Tang1, Kellen  M  Harkness1, Osman  M  Bakr3, Matthew  Pelton2, Francesco  Stellacci1.

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        Atomically monodisperse, thiolate-protected metal nanoparticles, containing on the order of 10 - 100 metal atoms, have been studied for several decades because of their unique and entirely novel optical, electronic, and structural properties. Recently, we developed a new method to create aryl thiol coated silver nanoparticles that show eight intense and broad non-plasmonic absorption bands with extinction cross-sections as high as 2.59 × 105 L mol-1 cm-1. Herein, we show these intensely and broadly absorbing nanoparticles (IBANs) are identified as a superatom complex with a molecular formula of [Ag44(SR)30]4- by sedimentation velocityanalytical ultracentrifugation (SV-AUC) and electrospray ionisation-mass spectrometry (ESI-MS). The unique time-dependent optical properties of IBANs are also invested by transient-absorption measurements. We observe two kinetic processes following ultrafast laser excitation of any of the absorption peaks: a rapid decay, with a time constant of 1 ps or less, and a slow decay, with a time constant that can be longer than 300 ns. The long lifetime of this state and the broad optical absorption spectrum mean that the ligand-stabilized silver clusters are promising materials for solar energy harvesting.

        8:00 PM - CC9.36

        Giant Fluorescence-intensity Enhancement as 7000-fold: Medusa-type Silver Nanoparticle Investigated by a Single Particle Spectroscopy and FDTD Calculations

        Hironori  Tamamitsu1, Hidemi  Suemori1, Ken-ichi  Saitow1 2.

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        When noble metal nanostructure is optically excited, localized surface plasmon is generated, which produces large electric field at the nanostructure surface. When a molecule near the surface is excited by such large localized electric field, fluorescence intensities increase dramatically. Thus, various research groups have reported fluorescence-intensity enhancement effect as metal-enhanced fluorescence (MEF). According to recent review articles on MEF, almost researches of MEF have been conducted using gold or silver nanoparticles, and a typical value of fluorescence-intensity enhancement factor (EF) has been 20. On the other hand, large EFs were reported using a bow-tie-shaped gold nanoantenna (EF=1340) and using bimetallic (Au/Ag) nanostructure (EF=4000). We have fabricated novel nanoparticles by conducting pulsed laser ablation in supercritical fluids. In our previous study, RGB-light-emitting, or white-light-emitting silicon quantum dots (Si-QDs) were synthesized. As the other system, silver (Ag) nanoparticle with a specific morphology was generated. That is, many nanochains are attached to a large Ag nanosphere with a diameter of 800 nm. This specific morphology was called Medusa-type nanoparticle, which was observed by pulsed laser ablation of gold. Thus, the Ag or Au Medusa-type nanoparticle showed very large EF of Surface Enhanced Raman Scattering (SERS), that is, the EF was an order of one billion. Here we show the experimental and theoretical study on the fluorescence-intensity enhancement using the Medusa-type Ag nanoparticles. Two systems were investigated. That is, the enhancement effects of fluorescence intensities of dye molecule of crystal violet (CV) and silicon quantum dot (Si-QD) were measured by a single Medusa-type nanoparticle using a microscopic spectroscopy. As a result, the obtained EFs of CV and Si-QD were 7000 and 30, respectively. Note that the value of 7000 is 7 times larger than the world record EF=1000 for Ag nanoparticle & dye molecules. As for the Si-QD, the value of 30 is 3 times larger than the typical EF=10 for Ag nanoparticle & Si-QDs. To investigate the reason for giving the giant EF of the Medusa-type nanoparticle, we performed the scattering spectral measurements of a single Medusa-type nanoparticle by microscopic spectroscopy. In addition, the localized electric field on the Medusa-type nanoparticle was theoretically quantified by the calculations based on Finite Difference Time Difference (FDTD) method. As a result, we revealed that the giant EF of Medusa-type Ag particle is brought from the localized electric field at branching and/or crossing point of many nanochains on the Medusa-type nanoparticle.

        8:00 PM - CC9.37

        Full Three-Dimensional Numerical Analysis of Far-field Radiation from a Plasmonic Nanoantenna

        Jinhyung  Kim1, Jung-Hwan  Song1, Kwang-Yong  Jeong1, Min-Kyo  Seo1.

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        Metallic nanostructures, referred to as optical nanoantennas, not only support plasmon resonances that confine lights in sub-wavelength dimensions but also convert freely-propagating optical radiation into a localized field and vice versa. In addition to the light confinement, it is required to control the far-field radiation of the nanoantennas to realize a functional and power-efficient optical nanodevice. For example, engineering fluorescent emission by a plasmonic antenna, such as a highly collimated beam, is expected to allow practical and fundamental applications in optical spectroscopy and sensing. It is well known that the far-field radiation from a plasmonic antenna is highly dependent on its structural geometry. In addition, the extraction and coupling efficiencies of a single emitter coupled to the nanoantenna are governed by three-dimensional local density of states (LDOS) according to the Fermi’s golden rule. Therefore, it is important to fully understand the characteristics of the plasmonic nanoantenna in the evanescent (non-radiative near-field), Fresnel (radiating near-field) and Fraunhofer (far-field) regions together with the substrate effects. Nevertheless, recent works about the power flow and far-field radiation from the antenna have focused on mainly one- or two-dimensional structures surrounded by a homogenous medium. Here we report the full three-dimensional numerical analysis of a gold nanodisk antenna coupled to a single dipolar emitter on a glass substrate using the finite-difference time-domain method. In order to examine the effect of the substrate as an inhomogeneous medium on the far-field radiation, we employed a novel near- to far-field transformation based on the reciprocity theorem. The nanodisk antenna with a diameter of 120 nm supports two possible resonant modes in the visible wavelength region: fundamental dipole and higher-order quadrupole modes. The two resonant modes show totally different near- and far-field distributions. The fundamental mode shows a directional far-field radiation which can be modified by varying the polarization and position of the emitter. On the other hand, the higher-order mode clearly shows its unique quadrupole radiation pattern. In particular, the transition of the far-field radiation pattern from the fundamental mode to the higher-order mode is successfully investigated depending on the wavelength of the dipolar emitter. We also quantified the emitter output power coupled to the antenna and re-radiated to the far-field via the antenna modes, and the spontaneous emission enhancement including various substrate indices (SiO2, HfO2 and TiO2) effects. We believe that this study would not only help in understanding the single emitter energy flow channeling to far-field via the nanoantenna but also offer a potential approach to the far-field control for a nanoscale optical device.

        8:00 PM - CC9.38

        Silver Decorated Carbon Nanospheres as Effective Visible Light Photocatalyst

        Bedanga  B  Sapkota1, Armstrong  Wilson1, Sanjay  R  Mishra1.

        Show Abstract

        Large industrial wastes, mainly aqueous toxic dyes such as Azo dyes, from textile industry are routinely poured out in water as waste. The widely used biological treatment of waste water is found ineffective in treating dye loaded water as these dyes are resistant to destruction through biological treatment using microbes. The advances in synthesis of nanoparticles opened up an alternative solution to waste water treatment. Since their discovery, carbon nanotubes (CNTs) have attracted considerable attention due to their large surface area, high mechanical strength and remarkable electrical conductivities. Their one dimension structure indicates tremendous potential for nanosize catalyst supporter [1,2]. On the other hand, silver nanoparticles exhibit considerable visible light and UV light absorption due to surface plasmon resonance effect and the interband transition of 4d electrons to the 5sp band, respectively. In the present work, silver nanoparticles were deposited on amorphous carbon nanosphere template. The template was derived via hydrothermal treatment of glucose at180 OC for eight hours. The carbon 330 nm nanospheres were dispersed in varying silver nitrate solution and heated in household microwave for six min. The silver nanoparticles loading on carbon template was changed via varying silver nitrate concentration (0.125, 0.250, 0.375 and 0.5 g). The C-Ag nanospheres were analyzed via SEM, TEM, XRD, and Uv-vis absorption spectroscopy. The average crystalline size of silver particles was found to be 21, 17, 14, and 11 nm. The photodegradation of methylene blue in the presence of C-Ag was assessed using ambient light. The photocatalysis rate was determined using first order kinetic equation. The rate constant 0.1681/min observed with C-Ag (0.5g) was found to surpass that of TiO2-Ag (0.139 /min)[3] and ZnO (0.019/min) [4] nanoparticles. These results indicate the use of C-Ag as effective photocatalysts under visible radiation and avoid need of UV radiation in the waste water treatement. References: [1] M.S.T. Goncalves, A.M.F. Oliveira-Campos, E.M.M.S. Pinto, P.M.S. Plasencia, M.J.R.P. Queiroz, Chemosphere, 39, 781 (1999). [2] K. Tanaka, K. Padermpole, T. Hisanaga, Water Res., 34, 327 (2000). [3] S.X. Liu, Z. P. Qu, X. W. Han, C. L. Sun, Catalysis Today, 93, 877 (2004). [4] S. Baruah, M. A. Mahmood, M. T. Zar, T. Bora, J. Dutta, B. J. Nanotechnol, 1, 14 (2010).

        8:00 PM - CC9.39

        A Versatile and Easily Implementable Analytical Optical Model for 2D Assemblies of Small Sized Metal Nanoparticles with Moderate Coverage

        Johann  Toudert1, Lionel  Simonot2, Sophie  Camelio2, David  Babonneau2.

        Show Abstract

        During the last decades, continuous experimental and theoretical efforts have been made in order to understand the optical properties of confined systems, such as nanoparticles (NPs) [1,2]. In this context, many works have been devoted to metal NPs, which can be elaborated in a controlled way, accurately characterized at the nanoscale, and whose optical response is dominated by localized surface plasmon resonances (LSPRs). LSPRs usually induce resonant absorption, scattering and near-field enhancement, whose spectral and spatial features are highly sensitive to the NPs size, shape and environment. These works, which have provided an important fundamental knowledge about the optical response of metal NPs, have also involved the development of models and calculation tools for correlating the LSPRs features to the NPs size, shape and environment. Today, numerical (classical or quantum) methods allow reliable simulations of the LSPRs features in a wide range of cases [2,3]. Nevertheless, in order to spare calculation time and resources, it is sometimes useful to use approximate analytical models, which even provide satisfactory quantitative predictions in specific cases [4,5]. Analytical models, based on closed-form equations and a few parameters, are specially desired for the fast extraction of nanostructural information from the macroscopic optical response of nanocomposite thin films consisting embedded or supported NPs. At such aim, we have developed an analytical effective medium model suitable to the case of complex 2D assemblies of NPs of small size and with a moderate coverage, embedded in a homogeneous host medium [6]. Calculations rely on the quasi-static coupled dipole approximation, each elementary building block of the 2D assembly being described by a quasi-static dipole polarizability tensor. Ellipsoidal NPs shapes, for instance, can thus be taken into account, with a random or preferential in-plane orientation, possibly with polydisperse size and shape distributions. We will present and illustrate the capabilities of this versatile model for simulating the optical response of 2D assemblies of metal NPs, and highlight its easy implementation to optical simulation software for multilayer thin films or vertical photonic structures. [1] U. Kreibig and M. Vollmer, Optical properties of metal clusters, Springer (1995) [2] N.J. Halas et al., Chem. Rev. 111 (2011) 3913 [3] E. Hao et al. J. Chem. Phys. 120 (2004) 357 [4] H. Kuwata et al. Appl. Phys. Lett. 83 (2003) 4625 [5] I. Zoric et al., ACS Nano 5 (2011) 2535 [6] J. Toudert et al., Phys. Rev. B (accepted)

        8:00 PM - CC9.40

        Spectral Changes of Au-Ag Core-shell Nanorods Induced by Electrochemical Reactions of Silver Shells

        Yuki  Hamasaki1, Yasuro  Niidome1 2, Naotoshi  Nakashima1 2 3.

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        Silver nanoparticles have been widely studied because of their remarkable optical properties. We have prepared uniform anisotropic Au-Ag core-shell nanorods. The core-shell nanorod has unique optical property, which shows four extinction bands in visible region. The optical property depends on the shape of the core-shell nanorods. Electrochemical reactions of silver are a convenient way to design the shapes of silver nanoparticles, because the redox reactions of silver are controllable in a solution. We deposited Au-Ag core-shell nanorods on transparent ITO plates and performed electrochemical reactions of the silver shells. Redox reactions of silver in an aqueous solution are strongly affected by anions in electrolytes. In this work, KCl, KBr, KNO3, KClO4 and K2HPO4/KH2PO4 (phosphate buffer) solutions were used for the measurements. Spectral changes accompanying the redox reactions were monitored using a multi-channel spectrophotometer. The in-situ observation revealed the details of the oxidation and the deposition of the silver shells. Cyclic voltammograms showed an oxidation peak of silver shells at +0. V vs. SCE and a reduction peak of silver ions at -0. V vs. SCE.. In the presence of phosphate ions, the observed spectral changes of the Au-Ag core-shell nanorods were reversible. The formation of insoluble Ag3PO4 on gold nanorods contributed to this reversible shell formation. In contrast, the other anions used did not suppress the diffusion of silver ions into the bulk solution, which were instead deposited as larger silver nanoparticles. It was found that the electrochemical responses of the core-shell nanorods could be controlled by the diffusion of silver ions and electrochemical deposition of metallic silver. The resulting combination of surface modification and controllable redox reaction will open up a new methodology to design functional silver nanoparticles that have tunable optical properties. If we can design an electrochemical reaction of uniform silver nanoparticles, it will be a useful method to obtain preferable optical properties.

        8:00 PM - CC9.41

        Galvanic Replacement as a Sink-source Method for Nano-scaled Material Deposition

        Kyle  D  Gilroy1, Pouyan  Farzinpour1, Aarthi  Sundar1, Robert  A.  Hughes1, Svetlana  Neretina1.

        Show Abstract

        Galvanic replacement is a chemical reaction that occurs when atoms of a solid metal, referred to as the template, react with the ions of a second metal in the solution phase. In general, if the second metal has a higher electrochemical potential, it results in a spontaneous oxidation-reduction reaction where this metal is reduced and deposited on the surface of the template as template atoms are simultaneously oxidized and dissolved into solution. Such replacement reactions have been adopted as a means to synthesize a myriad of uniquely shaped nanostructures with a wide range of optical properties. In a typical synthesis, the reaction between a colloidal template and the chemical reagent takes place in solution where the product is later isolated from suspension using a centrifuge and later dispersed onto a substrate for analysis. Only recently has this technique been utilized to manipulate the optical, chemical, and morphological aspects of templates which are directly attached to substrate. Here, we present a synthetic route capable of transforming periodic substrate-based silver nanostructure arrays into corresponding arrays of pure Au, Pd, and Pt. Morphologic and compositional changes were recorded using SEM, AFM and EDS. Thermal heating was then used to reform the product into a spherical nanostructure as well as rid the product of any remaining template atoms. This procedure is a viable solution for delivering small quantities of precious metal to site-specific locations. Since the amount of material delivered to a site can be regulated by reaction time, the diameter of the final product can be tuned. Control over the final diameter is demonstrated by monitoring the plasmon resonance and comparing this result with Discrete Dipole Approximation (DDA) simulations.

        8:00 PM - CC9.42

        Porosity Influence in the Optical Response of a Porous Silicon Gold Nanoparticle Plasmonic Material

        De la Mora  Mojica  Maria Beatriz1, Bornacelli  Jhovani1, Nava  Rocio2, Zanella  Rodolfo3, Reyes-Esqueda  Alejandro1.

        Show Abstract

        Metal nanoparticles on semiconductors are of interest due to the effect of surface plasmon resonance of free electrons, showing a strong absorption at specific wavelengths that depend on the particle size, shape, spatial distribution and substrate refractive index and electronic properties. In this work, colloidal gold nanoparticles, with an average size of 6.2 ± 3 nm, were added into luminescent porous silicon by drop casting. The gold nanoparticles interact with porous silicon by modifying its optical properties such as photoluminescence, reflectance and absorption. Here, we present a study about the influence of the porous silicon porosity in the final optical response of our hybrid porous silicon/gold nanoparticle plasmonic material. By varying the etching conditions, we propose the control of the porosity as a possible mechanism for tuning the optical response of the hybrid plasmonic material.

        8:00 PM - CC9.43

        Magnetic Quenching of Plasmon-photonic Response in Fe3O4-elastomer Composite

        Kofi  W.  Adu1 5, Pralav  P.  Shetty4, Dustin  T.  Hess2, Danhao  Ma3, Richard  C.  Bell7, Mauricio  Terrones1, Kathryn  J.  Carruba6.

        Show Abstract

        We report a systematic study of polarization dependence and the effect of particle size on the optical response of Fe3O4-silicone elastomer composites in the presence of external static magnetic field. The Fe3O4 particles were aligned in the elastomer matrix with the static magnetic field. The optical response of composites containing 2wt%, 5wt% and 15wt% of 20nm d 30nm, 40 nm d 60nm and d 500nm Fe3O4 particles were aligned in- and out-of-plane in the elastomer and the optical absorption were measured with an absorption spectrometer. We observed a systematic redshift in the optical response of the out-of-plane composite samples (containing nanoparticles 20nm d 30nm, 40 nm d 60nm) with increasing static magnetic field strength, which saturated near 600 Gauss. Furthermore, the observed redshift increased with increasing weight percent of Fe3O4 in the composite; obtaining a maximum shift of 174 nm at 600 Gauss in the 15wt% Fe3O4-elastomer composite films. The observed redshift in the optical response of the out-of-plane composite is attributed to the effect of magnetic field strength and the metal particle/cluster size in the elastomer. There were no observable shifts in the in-plane samples, suggesting that the orientation (polarization) of the magnetic dipole and the induced electric dipole play a crucial role in the optical response. However, we observed a dramatic suppression to near quenching of the plasmonic activities in the micron size particles (d < 500nm) elastomer composite. This occurred even at very low applied static magnetic fields, suggesting particle size limitations in modulation of plasmon-photonics by external magnetic field. Dipole approximation model is used to explain the quenching phenomenon.

        8:00 PM - CC9.44

        Plasmonic-Magnetic Au@Fe Core@Shell Nanoparticles

        Prerna  Singh1, Anh  Thi Ngoc  Dao1, Derrick  Mott1, Shinya  Maenosono1.

        Show Abstract

        An important research direction in nanomaterials synthesis is the expansion from single component nanoparticles to hybrid nanostructures. These heterostructured nanoparticles can exhibit distinct optical, catalytic or photocatalytic properties which offer tailoring or tunability. New nanoparticles that combine an optical signature with other physical properties are particularly useful, enabling optical addressability for sensing and diagnostics in addition to other properties. A very useful strategy for imparting optical properties at the nanoscale involves the integration of noble metals and their associated localized surface plasmonic properties into the particle structure. Gold nanoparticles have already been demonstrated for use in a wide range of applications including catalysis, bio-probes, optical devices etc. The coupling of Au nanoparticles with other metals such as Fe to form Au@Fe core@shell nanoparticles can allow the coupling of both optical and magnetic properties in a single functional probe. Building upon this idea, it has recently been demonstrated that a unique electronic interaction takes place between Au and Ag in the Au@Ag core@shell structure, which results in enhanced resistance to oxidation for the Ag. In light of these results, we performed a fundamental study to synthesize and fully characterize the Au@Fe nanoparticle system. The Au nanoparticles were synthesized in aqueous medium via the well-known citrate reduction method. These Au nanoparticles were used as monodispersed seeds for the further deposition of an Fe shell. The Fe was essentially grown on the Au nanoparticles surface via seed mediated growth to form Au@Fe NPs. The resulting nanoparticles morphology and structural properties were studied using TEM and STEM-HAADF revealing a discrete core@shell structure. UV-Vis was performed to study the plasmonic properties of the nanoparticles. The unique electronic properties for this system were studied using XPS. The magnetic properties of the nanoparticles were appraised using the SQUID technique. This presentation will focus on the synthetic technique towards multi-component plasmonic-magnetic nanoparticles composed of Au and Fe and will delineate the unique electronic interaction that exists at the interface of the two metals in the nanoparticle structure.

        8:00 PM - CC9.45

        Revealing Nonlinear Plasmon-photon Interactions Using k-space Spectroscopy

        Nicolai  B  Grosse1, Jan  Heckmann1, Ulrike  K.  Woggon1.

        Show Abstract

        Surface plasmon (SP) excitation in metal-dielectric structures is exemplified by an enhanced local electromagnetic field and SP-induced local field enhancements have found numerous applications. But ever since the first demonstration of SP-related second-harmonic generation (SHG) by Simon et al. [1], understanding the microscopic origin of the nonlinearity and the real impact of the presence of SP in the SHG process, has remained an active research topic. The role of SP in the process, whether as a field-enhancing catalyst or as a quasiparticle converted in the interaction, has remained experimentally elusive. In this contribution we identify the role of plasmons in nonlinear optical phenomena and show that surface plasmons do not simply modify photon interactions, but may directly combine and annihilate with other plasmons to create outgoing frequency doubled photons [2]. We present experimental results that reveal the plasmon-photon nonlinear interactions which are responsible for the enhanced SHG from a metal nano-film. What makes our approach distinctive is that we have revisited the pioneering experiments [1] where SP propagate with well-defined k-vectors on the surface of bulk metal; and that we have employed k-space spectroscopy in the Kretschmann geometry, to examine the emitted SHG in a way that provides precise information on SP nonlinear phase-matching. Because each type of nonlinear interaction conserves momentum, they can be distinguished by their unique signature in k-space. The SHG emission from a 60nm thin silver film (Kretschmann geometry) was mapped in k-space across exit angle as a function of input fundamental angle. Our experimental results show that for excitation angles in the vicinity of the SHG peak, there is an off-diagonal component which is consistent with the signature of the pp-f interaction. This is in contrast to the purely photonic ff-f interaction which lies on the diagonal. From these results, we conclude that plasmon-SHG is dominated by a process where two fundamental SP are converted to a second-harmonic photon (pp-f). Our results could enable design of new nanophotonic structures that strongly enhance the efficiency of nonlinear processes via plasmon-plasmon interactions. The results have furthermore implications for realizing the inverse process, plasmonic parametric downconversion, which could act as a coherent source of entangled surface plasmon pairs where one higher-energy photon is “downconverted” to two lower-energy plasmons. [1] H. J. Simon and J. G. Watson, Optical Second-Harmonic Generation with Surface Plasmons in Silver Films, Phys. Rev. Lett. 33, 1531 (1974) [2] N.B. Grosse, J. Heckmann, U. Woggon, Nonlinear Plasmon-Photon Interaction Resolved by k-Space Spectroscopy, Phys. Rev. Lett. 108, 136802 (2012)

        8:00 PM - CC9.46

        Coupled Quantum Emitters in Low Index Metamaterials; Concurrence and Quantum Superradiance

        Ruzan  Sokhoyan1, Harry  A.  Atwater1.

        Show Abstract

        It is well known that coupling of quantum emitters via a common reservoir results in effective interaction between the emitters. However for emitters in free space, these interactions drastically diminish when the inter-emitter spacing is increased to the order of half a resonant wavelength. Placing emitters inside a metamaterial could substantially increase their interaction range. In the present work we articulate how metamaterials, and in particular those with epsilon-near-zero could be used as a host medium for observation of quantum cooperative effects for dipole coupled emitters. We show that in these metamaterials the emitters interact strongly at distances greatly exceeding the free-space resonant wavelength. By considering spontaneous transition of the emitters embedded in the epsilon-near-zero materials, we show possibility of long-term entanglement of the emitters with large concurrence values attainment. By analyzing the expressions for the decay rates, collective coupling and collective damping parameters of the dipole emitters, we discuss the effect of the dissipation on the generation and preservation of the entanglement. Further, we survey the effect of the medium temperature on concurrence and determine the limiting temperature at which the emitters can still become entangled via spontaneous emission. When considering the possibility of the observation of Dicke superradiance [1], we show that emitters “sense” the electromagnetic field when placed in the lossless epsilon-near-zero materials, in the same way, independent of their spatial position, which is a necessary condition for observation of the superradiant pulse. Finally, using Green’s function formalism we discuss the dynamics of the coupled emitters for different geometries of the host metamaterial. We focus on the case of the stratified medium and consider planar, spherical, and cylindrical stratified structures. We analyze how the variation of the layer thicknesses of the stratified structures affects the temporal dynamics of the dipole emitters embedded in them. Lastly, details for nanoscale emitters such as single molecules and nitrogen vacancy centers in epsilon near zero metamaterials and plasmonic waveguides near cutoff will be presented. References [1] R.H. Dicke, Phys. Rev. 93, 99 (1954).

        8:00 PM - CC9.47

        Photon Antibunching of a Single Semiconductor Nanocrystal Interacting with the Localized Surface Plasmon of Metal Nanostructures

        Sadahiro  Masuo1, Hiroyuki  Naiki2, Yoshihisa  Uedao1, Keisuke  Kanetaka1, Akira  Itaya3.

        Show Abstract

        The use of semiconductor nanocrystals (NCs) as a material for the optoelectronic applications and biolabeling has been the focus of great attention. One of the interesting optical properties of single NCs is their photon antibunching, i.e., single-photon emission behavior at room temperature. However, single NCs show strong fluorescence blinking, which inhibits single-photon emission. It has been reported that this blinking behavior is strikingly suppressed by localized surface plasmon resonance (LSPR) in metal nanostructures. LSPR is also reported to give rise to an increase in the fluorescence intensity and a shortening of the lifetime, which is known as fluorescence enhancement. These effects are highly desirable for efficient single-photon sources. In recent years, a few reports about photon antibunching behavior of single NC-metal nanostructure systems have been published. However, a detail mechanism is still unclear. In this study, we investigated the photon antibunching behavior of single NCs (CdSe/ZnS core/shell NC) interacting with the LSPR of the metal nanostructures (silver and gold nanoparticles). By simultaneously measuring time traces of fluorescence intensity, lifetime, fluorescence spectra, and photon correlations of single NCs, we have revealed that the probability of single-photon emission strongly depended on the fluorescence lifetime, i.e., the probability of single-photon emission decreased when the lifetime was shorter than sub-ns. Based on the estimation of both radiative and non-radiative decay rates enhanced by LSPR, the following mechanism was proposed. In the absence of metal nanostructures, multiple excitons generated by a high-power excitation lead to single-photon emission via non-radiative Auger recombination process between the excitons. In the presence of metal nanostructures, even when the excitation power is low, multiple excitons are initially generated in a single NC by the enhanced electromagnetic field of the LSPR. Subsequently, a portion of these excitons radiatively decay via plasmon, i.e., the radiative decay rate enhanced by LSPR competes with the Auger recombination process. When the enhanced radiative decay rate is faster than that of the Auger process, multiphoton emission can be observed. Therefore, a decrease in the probability of single-photon emission is observed when the fluorescence lifetime is shortened. This result will improve our understanding of fluorescence enhancement by the LSPR of metal nanostructures, assist in the creation of effective single-photon sources, and allow for the utilization of the multiexcitons in NCs for optoelectronic applications.

        8:00 PM - CC9.49

        Single and Multiprobe Apertureless Thermal Imaging of Electromagnetic Excitation over a Wide Range of Wavelengths

        Aaron  Lewis1 2, Rimma  Dekhter3, Sofia  Kokotov3, Patricia  Hamra3, Boaz  Fleischman3, Hesham  Taha3.

        Show Abstract

        Near-field optical effects have generally been detected using photodetectors. There are no reports on the use of the temperature changes caused by electromagnetic radiation using thermal sensing probes for scanned probe microscopy. In this paper we apply our development of such probes to monitor the effects of electromagnetic radiation at a number of different wavelengths using the heating caused in a sample by specific wavelengths and their propagation. The paper will catalogue effects over a wide spectrum of wavelengths from the near to mid infrared. The method has been applied from devices to molecules. The thermal sensing probes are based on glass nanopipettes that have metal wires that make a contact at the very tip of a tapered glass structure. These probes are cantilevered and use normal force tuning fork methodology to bring them either into contact or near-contact since this feedback method has no jump to contact instability associated with it. Data will be shown that defines the resolution of such thermal sensing to at least the 32 nm level. In addition the probes have the important attribute of having a highly exposed tip that allows for either optical sensing methodologies with a lens either from directly above or below or heat sensing with a single or additional probe in a multiprobe scanning probe system. With such a system it will be shown that apertureless infrared excitation and detection can be affected and results will be shown on a variety of systems including devices and a suspended carbon nanotube. The approach described in this paper has considerable advantages over purely optical methods for both excitation and detection to which it can be directly compared.

        Download Session Locator (.pdf)2012-11-29  

        Symposium CC

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        Symposium Organizers

        • Matthew Doty, University of Delaware
        • Srikanth Singamaneni, Washington University
        • Andrey L. Rogach, City University of Hong Kong
        • Mark Brongersma, Stanford University
        • Vladimir V. Tsukruk, Georgia Institute of Technology

          CC10: Plasmonic Nanomaterials II

          • Chair: Younan Xia
          • Thursday AM, November 29, 2012
          • Hynes, Level 2, Room 208
           

          9:00 AM - *CC10.01

          Controlling the Shape of Silver Nanocrystals for Field Enhancement Application

          Younan  Xia1.

          Show Abstract

          This talk will discuss how the shape of a Ag nanocrystal can be controlled to maximize its capability to enhance local electric field. Specifically, I will focus on seed-mediated growth of Ag nanocrystals with defferent morphologies by using Ag nanocubes as the seeds. I will discuss how the growth habit of Ag cubic seeds can be controlled to maneuver the shape of Ag nanocrystals. By controlling the reaction parameters, including the ratio of Ag precursor to the seed, the capping agent, the reductant, and the foreign ions, we have successfully prepared a series of Ag nanocrystals with well-controlled shapes and sizes. The products include cubes, cuboctahedrons, octahedrons, octapods, trisoctahedrons, concave cuboctahedrons, and concave octahedrons. In addition to the synthetic protocols and mechanisms, I will also discuss the use of these nanocrystals in field enhancement applications in the contect of LSPR and SERS.

          9:30 AM - CC10.02

          Using Nonlinear Optical Hot Spots to Study Localized and Delocalized Plasmonic Excitations in Silver Nanoparticle Films

          Nicholas  J.  Borys1, Alex  Thiessen1, John  M.  Lupton1.

          Show Abstract

          In addition to being ideally suited for single-molecule surface-enhanced Raman (SERS) spectroscopy [1,2], rough silver films grown with the Tollens reaction show intrinsic nonlinear emission from discrete hot spots comprised of second-harmonic generation that blinks [3] and continuum emission that can be used for simple, but high resolution transmission microscopy [4]. By carefully controlling the silver film growth process, a wide range of structural morphologies of complex silver plasmonic nanosystems can be grown [5] that range from a dense packing of discrete silver nanoparticles that couple in the near and far-field radiation zones to semi-continuous rough silver films with optical responses that are defined by near-field coupling of their constituent nanoparticles. Single nonlinear hot spot microscopy of the different plasmonic film morphologies reveals different regimes of electromagnetic coupling that leads to the hot spot formation. In particular, nonlinear excitation spectroscopy and polarization anisotropy where the nonlinear emission intensity is recorded as a function of excitation energy and polarization, respectively, reveal broad resonances in the films of discrete nanoparticles that are reminiscent of localized surface plasmon modes, while the nonlinear hot spots in the semi-continuous metal films have multiple, surprisingly narrow resonances that reflect delocalized excitation of the hot spots mediated through propagating surface plasmons. The intermediate morphologies that bridge discrete nanoparticles and semi-continuous films show a smooth transition between the two extremes reflecting a possible hybridization of delocalized and localized plasmonic resonances. By combining the excitation spectroscopy of single nonlinear hot spots with both electron microscopy and localization microscopy with ~10 nm spatial resolution, structural profiles of the unique hot spots in all of the regimes are obtained. This approach establishes the foundation to build an extensive library of nanoparticle arrangements with documented excitation resonances and paves the way for careful engineering of well-defined plasmonic systems derived from the random metal films which give rise to some of the largest field enhancements necessary for applications such as single-molecule SERS [1,2]. [1] M. J. Walter et al., Phys. Rev. Lett. 98, 137401 (2007). [2] M. J. Walter et al., J. Am. Chem. Soc. 130, 16830 (2008). [3] N. J. Borys et al., Phys. Rev. B 80, 161407(R) (2009). [4] D. Chaudhuri et al., Nano Lett. 9, 952 (2009). [5] N. J. Borys et al., J. Phys. Chem. C 115, 13645 (2011).

          9:45 AM - CC10.03

          Optical Engineering with Templated Self-assembled Metallic Nanoclusters

          Jonathan  Albert  Fan1, Kui  Bao2, Li  Sun1, Jiming  Bao3, Vinothan  N.  Manoharan1 4, Peter  Nordlander2, Federico  Capasso1.

          Show Abstract

          In contrast to electronics, which features elements in the nanometer regime, the size of optical components has been inherently limited by the wavelength of light. Recent demonstrations of metallic nanostructures that support plasmons have pushed over this boundary. Plasmons are collective oscillations of free electrons driven by electromagnetic waves. When light is coupled to isolated metallic nanostructures, localized surface plasmon resonances(LSPR) are excited which create unique near- and far-field properties. Plasmonic nanoparticle assemblies can serve as a platform in which optical resonances, and hence the near-field intensity distributions, can be precisely tailored by the number, position, and shape of nanoparticles in a cluster. These metallic nanostructures have traditionally been fabricated with lithographic techniques whose planar nature limits the type of structures that can be achieved. One alternate technique that can overcome some of the limitations of lithography is templated self-assembly (TSA), which is a bottom up method that allows for the construction of large arrays of particle clusters based on a pre-designed template. In this report, we show that a broad range of plasmonic nanoshell clusters can be assembled onto lithographically-defined elastomeric substrates with relatively high yields using TSA. We assemble and measure the optical properties of three cluster types: heptamers which demonstrate Fanoresonance dips, linear chains that work as linear antennas, and rings of nanoparticles which exhibit strong magnetic properties. The assembly of plasmonic nanoclusters on an elastomer paves the way for new classes of reconfigurable plasmonic devices and optical metamaterials that can be transfer-printed onto various substrate mediums.

          10:00 AM -

          Break

          Show Abstract

          10:30 AM - CC10.04

          Symmetry Breaking of Silver Nanocubes: Higher Multipolar Cube Modes for Chemical Sensing

          Tobias  AF  Konig1, Rajesh  Kodiyath1, Mahmoud  A  Mahmoud2, Mostafa  A  El-Sayed2, Vladimir  V  Tsukruk1.

          Show Abstract

          We studied how the present of a substrate in close contact to silver nanocube might break the symmetry of the local surface plasmon resonance (LSPR) modes. The resonant coupling could be controlled by distance between nanocube and refractive properties substrate, by different dielectric properties of environments, and by the shape of the nanocubes. In this work, we considered silver nanocubes to investigate the resonance changes caused by symmetry breaking in close contact with glass surface, high index substrate such as alumina and rounded alumina substrat. We present experimental measurements and numerical simulations based on the FDTD method which consider LSPR variations as caused by interaction from primitive dipole mode with higher multipolar nanocube modes. Instead of using the primitive modes for sensing application in this work we focus on higher multipolar cube modes as potential mode for higher sensitivity. In fact, our calculations show that the higher nanocube LSPR modes show much higher sensitivity compare to sensing with the primitive mode and about factor 4 higher figure of merit.

          10:45 AM - CC10.05

          Dynamic Templating: A New Pathway for the Assembly of Large-area Nanostructured Arrays

          Svetlana  Neretina1, Pouyan  Farzinpour1, Aarthi  Sundar1, Kyle  D.  Gilroy1, Robert  A.  Hughes1.

          Show Abstract

          A substrate-based templated assembly route has been devised which offers large-area, high-throughput capabilities for the fabrication of periodic arrays of sub-micrometer and nanometer-scale structures. The approach overcomes a significant technological barrier to the widespread use of substrate-based templated assembly by eliminating the need for periodic templates having nanoscale features. Instead, it relies upon the use of a dynamic template with dimensions that evolve in time from easily fabricated micrometer dimensions to those on the nanoscale as the assembly process proceeds. The route is based on the discovery that the dewetting characteristics of ultrathin films can be dramatically altered when the film is placed not on the bare substrate, but on a sacrificial layer which simultaneously evaporates or sublimates. This alteration can result in orders of magnitude enhancements to the areal extent over which the film agglomerates. Directing this assembly process through the use of shadow masks which define an array of pedestals of the sacrificial layer upon which the agglomerating material is deposited leads to the formation of nanostructured arrays. Moreover, the same shadow mask can be used to fabricate nanostructures of different sizes by merely adjusting the amount of material placed on the pedestal. Demonstrations of the technique have yielded large-area gold nanoparticle arrays having nanostructure dimensions as small as 18 nm. The route also has broad applicability, having already produced arrays of gold, silver, copper, platinum, nickel, cobalt, germanium and Au-Ag alloys on substrates as diverse as silicon, sapphire, silicon-carbide and glass.

          11:00 AM - CC10.06

          Influence of the Geometric Arrangement of Plasmonics Nanoaggregates on Their LSPR, Electromagnetic Hot Sites and Spectroscopic Applications

          Li-Lin  Tay1, John  Hulse1, Jeff  Fraser1.

          Show Abstract

          Coupling of the localized surface plasmon resonances within small aggregates of plasmonic nanoparticles is known to induce intense and localized electromagnetic hot-sites that are chiefly responsible for a family of surface enhanced spectroscopies. Experimental measurements and theoretical calculations have shown the intricate dependency of LSPR on the geometrical arrangement of nanoparticle structures but few have the relative electronic field strength at the various electromagnetic hot-sites. In this paper we investigate electric field hot sites in nanoparticle aggregates both by spectroscopic measurement and electromagnetic calculations. It is well recognized that the electromagnetic hot-sites in NP aggregates are of paramount importance in inducing strong SERS activity. This makes SERS an ideal technique for probing these electromagnetic hot-sites. Since the enhancement response in SERS is proportional to the fourth power of the local electric field, the molecules situated at the EM hot-sites will easily dominate the Raman spectrum of an adsorbate on NP aggregate. Observed variability of SERS strength between NP aggregates has often been portrayed as evidence of the irreproducibility of SERS on a NP substrate. However, this variation in SERS strength is actually a manifestation of the variability of electromagnetic field strength at the hot-sites in the various nanoaggregates assemblies. We have recently reported an experimental quantification of this SERS variability by correlating measured SERS signals of specific small NP aggregates with their geometric arrangements. Experimental measurements of LSPR and SERS were obtained through dark-field microscopy and Raman spectroscopy while structural geometry of the NP aggregates was elucidated with scanning electron microscopy (SEM). We also carried out comprehensive electromagnetic calculations using the discrete dipole approximation (DDA) to provide insights and guide our interpretations of experimental results.

          11:15 AM - CC10.07

          Plasmonic Nanoparticles Enhanced and Extended Performance of Light-sensitive Nanocrystal Skins

          Shahab  Akhavan1, Kivanç  Güngör1, Hilmi Volkan  Demir1 2.

          Show Abstract

          Chemically synthesized nanocrystals (NCs) are considered as promising materials for integrating them into the optoelectronic devices due to their bandgap tunability, easily depositing via spray coating, dip-coat and spin- coat at reduced costs over large area where lattice mismatch does not arise. Large area (48 cm2) and semi-transparent light sensitive nanocrystal skin (LS-NS) is demonstrated via spray-coating nanocrystals on top of polyelectrolyte-polymers based on photogenerated potential buildup, which is highly sensitive to UV and visible light. These LS-NS devices are operated on the basis of photogenerated potential buildup readout, as opposed to conventional charge collection. High sensitivity in the absence of external bias is due to the close interaction of NCs with the top contact while the other part is isolated using high dielectric spacing layer. Furthermore, monolayer of NCs, make the device semi-transparent with sufficient absorption, reduce noise generation and dark current. However, NCs show small absorption at long wavelength region, which limited the device performance. To enhance the sensitivity and operational range extension, embedding silver nanoisland into LS-NS is demonstrated. Using metallic Ag nanoisland, we optimized the localized plasmonic enhancement by tuning the plasmonic resonance and spacing between the plasmonic structure and semiconductor materials to prevent quenching. Various bilayers of polyelectrolyte polymers (PDDA and PSS) deposited on 1 nm Al2O3 as interparticle distance between metal nanoparticle and NCs to facilitate the effects of distance dependent behavior on localized plasmonic enhancement. Consequently, we found localized plasmon enhancement is possible for spacing about 8-15 nm in our device. We observed, 10 nm spacing to be optimal in which 153 % sensitivity enhancement observed compared to the bare case. Hence device operation was extended to further 100 nm wavelength region. Consequently, presence of metal nanoparticle result in enhanced absorption of the CdTe NCs film to generate more electrons and holes. As a result, more voltage buildup can be made to enhance the sensitivity of the device.

          11:30 AM - CC10.08

          Tunable Plasmonic Resonances in Self-assembled Binary Nanocrystal Superlattices

          Xingchen  Ye1, Jun  Chen2, Christopher  B  Murray1 2.

          Show Abstract

          Self-assembly of multicomponent colloidal nanocrystals (NCs) into large area ordered arrays provides a bottom-up approach for the fabrication of plasmonic metamaterials that might exhibit intriguing optical properties such as negative index of refraction, emerging optical magnetism and macroscopic visible-frequency invisibility. In this talk, we will present experimental studies on the plasmonic resonance of self-assembled noble metal-nonmetallic binary nanocrystal superlattices (BNSLs). An interfacial assembly method is used to organize these NCs into superlattices over centimeter-scale areas, which were then transferred onto optically-transparent substrates for microspectrophotometric measurements on individual superlattice domains (grains). By changing the NC composition and size ratio between the large and small NCs, we demonstrate that the plasmonic resonance of BNSLs is strongly dependent upon the lattice constants and symmetry and is broadly tunable over the entire visible frequency. We will also discuss some progress towards self-assembled reconfigurable metamaterials through controlled transformation of BNSLs.

          11:45 AM - CC10.09

          A New Approach for Elaborating and Designing Plasmonic Nanostructures for Spectroscopy Enhancement and High Contrast Imaging

          Caroline  Bonafos1, Patrizio  Benzo1, Maxime  Bayle1, Robert  Carles1, Gérard  Benassayag1, Béatrice  Pecassou1, Antoine  Zwick1.

          Show Abstract

          The limitation for fabricating molecular plasmonic substrates is due to the drastic requirement of controlling, on large areas in a reproducible way, a well-defined spacing between metallic nanostructures and molecules: their mutual interaction is indeed governed by the local topography of the electromagnetic field. A strategy to design and fabricate hybrid metallic-dielectric substrates for optical spectroscopy and imaging is proposed, based on an original technique, low energy ion implantation beam synthesis (LE-IBS) for the wafer-scale fabrication of Ag nanocrystals (Ag-NCs) planar arrays embedded in silica and silicon nitride layers on a silicon substrate [1]. By coupling this technique to micro fabricated stencils used as templates, we precisely control the size, density, and location of silver nanoparticles in the dielectric matrix. By coupling ballistic simulations and TEM observations we showed that sputtering and diffusion effects are the limiting phenomena for the control of the size, position and volume amount of NCs. Concerning NC stability, we demonstrate that post-annealing process strongly limits silver oxidation, which otherwise excludes the use of Ag NCs on free surfaces [2]. Different architectures consisting of three dimensional patterns of metallic nanoparticles embedded in dielectric layers are hence conceived to simultaneously exploit the optical interference phenomenon in stratified media and localized surface plasmon resonances on metal nanoparticles. These structures are based on a simultaneous control of opto-electronic properties at 3 scales (3S) (~ 2 / 20 / 200 nm) and along 3 directions (3D). Elastic (Rayleigh) and inelastic (Raman) scattering imaging assisted by simulations were used to analyze the optical response of these “3S-3D” patterned layers. The reflectance contrast is strongly enhanced when resonance conditions between the stationary electromagnetic field in the dielectric matrix and the localized plasmon resonance in the silver nanoparticles are realized [3]. These novel kinds of plasmonic-photonic architectures are reproducible and stable, they preserve flat and chemically uniform surfaces, offering opportunities for the development of efficient and reusable substrates for optical spectroscopy enhancement (like SERS) and high contrast imaging. [1] R. Carles, C. Farcau, C. Bonafos, G. Benassayag, B. Pécassou and A. Zwick Nanotechnology 20, 355305 (2009). [2] P. Benzo, L. Cattaneo, C. Farcau, A. Andreozzi, M. Perego, G. Benassayag, B. Pécassou, R. Carles and C. Bonafos J. Appl. Phys. 109, 103524 (2011). [3] R. Carles, C. Farcau, C. Bonafos, G. Benassayag, M. Bayle, P. Benzo, J. Groenen, and A. Zwick ACS Nano 5, 8774 (2011).

          CC11: Plasmonic and Bioapplications

          • Chair: Vladimir Tsukruk
          • Thursday PM, November 29, 2012
          • Hynes, Level 2, Room 208
           

          1:30 PM - *CC11.01

          Targeting with Plasmonically Enhanced Scattering Nanoparticles Changes Cell Functions and Unravels Its Secrets1-4

          Mostafa  El-Sayed1.

          Show Abstract

          Using biochemical-targeting methods, one can conjugate the plasmonic nanoparticles to many parts of the cell, healthy or sick. Since the nanoparticles have comparable size to many parts of the cell, binding plasmonic (or nonplasmonic) nanoparticles to parts of the cell could change their properties including curing, or, most likely, killing sick cells. Using plasmonic nanoparticles has the advantage of using their enhanced scattering to image the response of the cells (including their death) to the effect of binding the nanoparticles to the selected part of the cell. Not only one can image the response of the cells directly bound to the nanoparticles but also the reaction of the community of the surrounding nanoparticle-free cells. References: (1) Kang, B.; Mackey, M. A.; El-Sayed, M. A. J. Am. Chem. Soc Comm. 2010, 132, 1517 (2) Austin, L.; Kang, B.; Yen, C.-W.; El-Sayed, M. A. J. Am. Chem. Soc. 2011, 133, 17594. (3) Austin, L. A.; Kang, B.; Yen, C.-W.; El-Sayed, M. A. Bioconjugate Chem. 2011, 22, 2324. (4) Kang,B, Austin, L.A., M. A..El-Sayed, Nano-letters, Submitted.

          2:00 PM - CC11.02

          Plasmonic Diatom Bio-nanostructures for Enhanced Light Harvesting Properties

          Julien  Romann1, Arne  Royset2, Gabriella  Tranell1, Mari-Ann  Einarsrud1.

          Show Abstract

          Diatoms are single-celled algae which produce nanostructured silica (SiO2) "frustules" through biomineralization processes. These frustules present special optical properties induced by their intricate 3D morphology, making them very interesting for light harvesting purposes. Their optical behavior can be described as a photonic band structure, making these frustules equivalent to photonic crystals. A key challenge is to both improve and control the optical properties of the frustules. The aim of the present work is to demonstrate that such a challenge can be solved by plasmonic enhancement. Some metallic nanostructures, including gold and silver nanoparticles, are well known for generating Local Surface Plasmon Resonance (LSPR) in the visible spectral range. Combining the light channeling properties of photonic crystals with plasmonic nanoparticles (NPs) offers a unique opportunity to turn frustules into active optical enhancers, with great potential for photovoltaics, sensors and enhanced Raman scattering applications. Another aspect lies in the high specific surface conveyed by the nanoporous structure of the frustules. These objects allow a high density of deposited NPs and can be considered as 3D substrates. Indeed, a layer of plasmonic NPs-decorated frustules features a much higher surface density of NPs than most standard plasmon enhanced substrates. The present work first focuses on the elaboration of plasmonic bio-synthesized nanostructures by decorating frustules with plasma sputtered gold NPs. Although the plasma sputtering method does not provide any control over the shape of the gold NPs, it is simple and fast. Because gold spreads and forms a continuous layer when directly deposited on the silica surface of frustules, two different methods are compared to obtain individual gold NPs instead. One known method is thermal dewetting of a plasma sputtered gold layer on silica frustules. By dewetting at 700 °C a previously sputtered 5 nm-thick gold layer, gold NPs of 20 nm are easily obtained on the frustules surface. Moreover, the thickness of the sputtered layer appears to be a good control parameter to obtain different NP sizes and size distributions. The second method consists of pre-coating the frustules with a layer of polyethylene glycol (PEG) before sputtering gold on top of it. The PEG layer shows a remarkable stabilizing effect also leading to gold NPs of around 20 nm on the frustules surface. Characterizing the optical properties of the modified frustules is the second focus of this work. The plasmon absorption induced by the gold NPs is highlighted by UV-visible absorption analysis of the gold-decorated frustules. Additionally, diffraction from the frustules can be observed by spectrophotogoniometry. This is a very good example of how to obtain combined optical properties by slightly modifying complex bio-synthesized nanostructures.

          2:15 PM - CC11.03

          Bio-inspired Band-gap Tunable Elastic Photonic Fibers

          Mathias  Kolle1, Alfred  Lethbridge2, Moritz  Kreysing3, Jeremy  Baumberg4, Peter  Vukusic2, Joanna  Aizenberg1.

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          Biological photonic structures that are at the origin of structural color have been found in a variety of land-, air- and seaborne animals. By contrast, only a few plants are known to involve photonic structures in their interaction with light. To this end we present the investigation of the photonic system found in the shiny blue seeds of a tropical plant. The strong nearly isotropic color results from the interaction of light with a hierarchical structure found inside individual tissue cells, consisting of concentrically arranged regular layers. This unique photonic architecture inspired the creation of a novel artificial photonic fibre system, exploiting the main features of the plant’s photonic structure: nanoscale regularity superposed by a microscale curvature. A variety of fiber designs have been realized using a scalable technique that can be applied to make fibers from a wide range of materials with different optical and mechanical properties. We present a detailed experimental and simulation-based characterization of the fibers. Special attention is given to fibers made from elastic materials that show a large tuning range of over 200nm in their spectral band-gap position when a longitudinal mechanical strain is applied.

          2:30 PM - CC11.04

          Plasmonic Paper Based Localized Surface Plasmon Resonance Biosensor

          Limei  Tian1, Ramesh  Kattumenu1, Naveen  Gandra1, Srikanth  Singamaneni1.

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          State of the art localized surface plasmon resonance biosensors rely on plasmonic nanostructures on rigid solid substrates as spectrally homogenous transduction platform. While such substrates are sufficient for vapor and liquid phase sensing, they are not amenable for trace detection on solid surfaces. Here, we demonstrate that a common filter paper uniformly adsorbed with biofunctionalized plasmonic nanostructures can serve as a flexible substrate for collection and detection of trace amounts of bioanalytes (few µg) on real-world surfaces. Compared to conventional rigid substrates, bioplasmonic paper offers numerous advantages such as high specific surface area (resulting in large dynamic range), excellent wicking properties (naturally microfluidic), mechanical flexibility, compatibility with conventional printing approaches (enabling multiplexed detection and multi-marker biochips), and significant reduction in cost.

          2:45 PM - CC11.05

          Nanoscale Plasmonic Interferometry for Biosensing

          Jing  Feng1, Vince  S.  Siu1 2, Alec  Roelke1, G. Tayhas  R.  Palmore1 2 3, Domenico  Pacifici1 2.

          Show Abstract

          Optical scatterers such as nano-holes, grooves or slits etched in a metal film are efficient sources of propagating surface plasmon polaritons (SPPs). Interference between SPP waves excited by a scatterer array can lead to unprecedented control of light at nanoscale, e.g. higher-efficiency solar cells, surface enhanced Raman scattering, and compact biochemical sensors. Plasmonic interferometry has the potential to bring the advantages of conventional optical interferometry to micro- and nano-scale, promising for high-throughput, real-time biochemical monitoring. Here we propose the detection of light transmission through a dense array of plasmonic interferometers as a novel optical technique to measure the dispersion of any dielectric deposited on the metal surface, over small area (<10 µm2) and volume (as low as femtoliters). A typical plasmonic interferometer consists of a groove-slit pair etched in a metal film. A broadband beam incident on the groove excites SPPs propagating toward the slit, where interference with the incident beam occurs. Light intensity transmitted through the slit of each interferometer carries information about the effective SPP excitation efficiency β due to diffractive scattering by the groove, and the propagating phase dependent on refractive index of the dielectric. Measuring and stacking light intensity spectra by increasing groove-slit distance in the range of 0.25 - 10 µm, a color map, unique for the particular metal/dielectric combination, can be generated. Color maps for different interfaces, i.e. Ag/air, Ag/water and Ag/40wt% glucose in an aqueous solution were obtained experimentally. A “cut” in the color map at a wavelength can reveal an intensity profile at this specific wavelength. The difference between intensity maxima and minima is proportional to β. The relationship between effective excitation efficiency and wavelength at Ag/air interface was determined as: β = 128.2 /λ (λ in nm). In principle, this technique can be employed to determine β at any wavelength, for any groove, or any metal/dielectric combination. The dispersion of the refractive index for Ag, water and glucose in an aqueous solution were derived from analysis of the color maps. A database for the dispersion of different materials can be established in a similar fashion, leading to label-free biosensing applications. We recently published a paper describing a proof-of-concept sensing capability of plasmonic interferometry for glucose sensing. In conclusion, SPP excitation mechanism is illustrated by studying the optical performance of a plasmonic interferometer array. The effects of varying different key parameters on the optical property of plasmonic interferometers and a comparison between experimental and FDTD simulation results will be discussed. Our findings show that plasmonic interferometry is an alternative optical technique for accurately analyze thin dielectric films at multi-wavelength over a small area.

          3:00 PM -

          Break

          Show Abstract

          3:30 PM - *CC11.06

          Optomechanics with Functionalized Gold Nanoparticles

          Jochen  Feldmann1.

          Show Abstract

          TBD

          4:00 PM - CC11.07

          Improving Transfer Efficiency of DNA-organized Nanostructures

          Susan  Buckhout-White1 4, W. Russ  Algar1, Christopher  Spillman1, Joesph  Melinger2, Ellen  Goldman1, Mario  Ancona3, Igor  Medintz1.

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          With the ultimate goal of developing improved fluorescence resonance energy transfer (FRET) networks for characterization and control at the nanoscale, we have been utilizing DNA to build optically active nanostructures that are easy to design, fabricate, and reconfigure. This work utilizes the powerful techniques of structural DNA technology as developed by Seeman and others together with well-established ligation chemistries to prescriptively space dyes with a resolution approaching the limit set by the spacing between nucleotides. The nanostructures to be reported on range from simple linear wires to complex 3-dimensional structures, all of which are constructed from a common set of components and tested under identical conditions with the goal of understanding the factors that determine the end-to-end transfer efficiency. To investigate transfer efficiency in FRET networks we developed a series of DNA structures that probe either single FRET transfers from Cy3 donors to a Cy5 acceptor or 4-step FRET cascades involving Cy3, Cy 3.5, Cy5 and Cy5.5. We have studied linear and bidirectional arrangements as well as 4-way and 8-way junctions in order to look at the effect multiple donors have on increasing the output of the final acceptor. Within each of these structures we have varied the distance between the dyes to determine the optimal spacing enhanced FRET efficiency. We have also designed a series of DNA dendrimers to create a true funneling effect. Results from the pair wise data indicate that the 4 way structures show the greatest acceptor output with equal or slightly less from the 8-way structure. The dendrimer structure, having the same number of initial donors as the 8 way cascade, appears to mitigate this limitation by optimizing the enhancement at each step of the cascade. Overall this study looks to exploit the power of structural DNA technology to explore the space of FRET networks and frame design rules for achieving optimal transfer efficiencies.

          4:15 PM - CC11.08

          ``Clicked'' Plasmonic Core-satellites: Covalently Assembled Gold Nanostructures for Subcellular Raman Imaging

          Naveen  Gandra1, Srikanth  Singamaneni1.

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          Owing to virtually unlimited multiplexing ability and excellent photostability, Raman scattering based bioimaging is gaining immense attention. Design and synthesis of Raman probes, which exhibit large and uniform Raman signature is paramount in advancing this novel bioimaging modality. Surface enhanced Raman scattering probes in which a Raman marker is trapped at the interstices of closely spaced metal nanostructures is a powerful class of Raman probes. Core-satellite plasmonic nanoassemblies are ideally suited for SERS probes considering the isotropic and large SERS signals from such structures. Recently, we have demonstrated non-covalent assembly of shape-controlled plasmonic nanostructures into highly Raman-active core-satellite structures. However, these structures are not ideal for bioimaging due to their poor stability in physiological conditions. To overcome the aforementioned issue, we demonstrate covalently bonded isotropic core-satellite nanostructures using “click” approach. Although click chemistry is has been widely used as a synthetic technique, it has not been explored in the context of metal nanostructure assemblies. Here, to the best of our knowledge, for the first time, we demonstrate core-satellite nanoparticles using click chemistry. To obtain these structures, the individual cores and satellites are modified with two custom made click molecules with inbuilt Raman reporter. Subsequently, the surface modified nanoparticles are catalyzed by CuSO4.5H2O and sodium ascorbate to form a five membered azide ring through Huisgen, 1,3-dipolar cycloaddition of alkyne and azide. Furthermore, these covalently assembled nanostructures are protected with SH-PEG-NH2 to increase the serum stability for both in vitro and in vivo applications. Finally, we demonstrate in vitro Raman imaging of SKBR3 cells using ERBB2 antibody functionalized core-satellites. Our studies lay the path forward for achieving highly stable, efficient, and cost-effective Raman probes for sub-cellular probing, bio-sensing and in vivo imaging.

          4:30 PM - CC11.09

          Optical Nano-imaging of Gate-tuneable Graphene Plasmons

          Jianing  Chen1 5 6, Michela  Badioli2, Pablo  Alonso-Gonzalez1, Sukosin  Thongrattanasiri3, Florian  Huth1 7, Johann  Osmond2, Marko  Spasenovic2, Alba  Centeno8, Amaia  Pesquera8, Philippe  Godignon9, Amaia  Zurutuza8, Nicolas  Camara10, Javier  Garcia de Abajo3, Rainer  Hillenbrand1 4, Frank  Koppens2.

          Show Abstract

          Graphene holds great promise for ultra-compact and electronically controlled plasmonics [1,2]. Recently, resonant coupling of propagating THz waves to plasmons in micro-ribbons has been demonstrated [3], while IR near-field microscopy has been applied to observe the coupling of graphene plasmons to phonons [4]. In our work [5] we use (similar to ref. [6]) scattering-type scanning near-field optical microscopy (s-SNOM) to visualize propagating and localized infrared plasmon modes in graphene nanostructures in real space. By spectroscopic imaging we measure the graphene plasmon wavelength λp as a function of excitation wavelength, which confirms the theoretically predicted plasmon dispersion. We observe that the plasmon wavelength λp=λ0/40 is remarkably reduced compared to the illumination wavelength λ0, which can directly be attributed to the two-dimensionality and unique conductance properties of graphene. Furthermore, we demonstrate tunability of the plasmon wavelength by gating graphene nanoribbons on a SiO2 substrate. The possibility to tune plasmons of extreme subwavelength electronically opens up a new paradigm in optical and opto-electronic telecommunications and information processing. [1] A. Vakil, N. Engheta, Science 332, 1291-1294 (2011) [2] F.H.L. Koppens, D.E. Chang, J. Garcia de Abajo, Nano lett. 11, 3370 (2011) [3] L. JU, et al., Nat. Nanotech. 6, 630 (2011) [4] Z. Fei, et al., Nano Lett. 11, 4701 (2011) [5] J. Chen, et al., , Nature doi:10.1038, 11254 (2012) [6] Z. Fei, et al., , Nature doi:10.1038, 11253 (2012)

          4:45 PM - CC11.10

          Tunable Graphene Plasmonic Devices for Terahertz Applications

          Jared  Strait1, Parinita  Sunil  Nene1, Weimin  Chan1, Jin-sung  Kim1, Haining  Wang1, Christina  Manolatou1, Joshua  Kevek2, Paul  McEuen2, Farhan  Rana1.

          Show Abstract

          Graphene, a two-dimensional atomic layer of carbon atoms, is particularly promising for plasmonics for three main reasons: i) the charge density, and hence the plasmon frequency is widely tunable by doping and electrostatic gating from 1 to 100 THz, ii) plasmon losses can be extremely small in graphene due to its high electron mobility, and iii) at large carrier densities, the plasmon oscillator strength in graphene is larger than any other known material due to its unique band structure and this means that plasmons in graphene are robust against decay. Thus, compared to the more common metal plasmonic materials, graphene offers frequency tunability, lower losses, and terahertz frequency operation, each of which broadens the application space for plasmonics [1-3]. In this talk we will present experimental results on some basic graphene terahertz plasmonic devices. Microfabricated graphene microstructures, such as strips, discs, rings, etc., confine plasmon modes and make it possible to excite these modes by free-space radiation. Graphene used in our work was grown by chemical vapor deposition (CVD) on centimeter-scale copper foils and then transferred onto Silicon and quartz substrates. Photolithography and oxygen etching was used to define graphene microstructures. Patterned graphene was doped by exposing to Nitric acid in order to adjust the carrier density. Electrostatic doping was also employed. Measurements were performed using a far-IR FTIR with a silicon bolometer detector. Measurements on graphene strips show that when the incident radiation is polarized perpendicular to the strip the confined plasmon resonance is excited and appears as a strong narrow peak in the absorption spectrum. We have developed an electromagnetic FDTD model that captures the frequency-dependent graphene conductivity to simulate the fabricated plasmonic structures. Fabricated micron scale wide graphene strips exhibit plasmon resonances in the 4-5 THz range for carrier densities in the 5E12-8E12 /sq-cm range. Comparison of simulations and measurements enables us to extract the carrier scattering time, the carrier density, and the carrier mobility values from measurements of plasmon resonance spectra. Scattering times and mobility values of 50-75 fs and 1700-2800 sq-cm/V-s were extracted at room temperature using this method and these values agree well with the typical reported values for CVD graphene. Much higher plasmon frequencies are obtainable in smaller microstructures. Simulations show that plasmon resonances in closely located microstructures interact strongly and therefore the measured frequency splittings can be used to study the strength of these interactions and realize novel plasmonic structures. In this talk, we will present experimental results for various graphene based plasmonic microstructures at different temperatures. [1] Nature Nanotech., 6, 630-634 (2011); [2] Nature Nanotech., 7, 330-334 (2012); [3] Nature Nanotech., 6, 611-612(2011)

          CC12: Poster Session: Optical Materials and Devices IV

          • Thursday PM, November 29, 2012
          • Hynes, Level 2, Hall D
           

          8:00 PM - CC12.01

          Giant and Large-area Uniform Enhancement of Fluorescence and Immunoassay by 3D Plasmonic NanoCavity Array and Fabricated by Nanoimprint

          Stephen  Y.  Chou1, Fei  Ding1, Wei  Ding1, Hao  Chen1, Weihua  Zhang1, Liangcheng  Zhou1.

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          Fluorescence plays a key role in many important disciplines. Metallic nanostructures can enhance fluorescence signals, but previous reported enhancements are low in average (over an area), and relatively high only at a few random "hot spots". Here, we report the a new plasmonic nanostructure -- disk-coupled dots-on-pillar antenna array (D2PA) [1] -- which has demonstrated (i) an unprecedented high fluorescence enhancement of an IR dye indocyanine green (ICG): 3,000-fold enhancement for an area average, 4×10^6-fold for a single dye molecule at a "hot spot", and an excellent large-area uniformity (for the average fluorescence) of a spatial variation <11% [2]; and (ii) enhancement of the average fluorescence of an immunoassay of Protein A and human immunoglobulin G (IgG) by over 7400-fold and the immunoassay’s detection sensitivity by 3 000 000-fold (the limit of detection is reduced from 0.9 ×10^−9 to 0.3 × 10^−15 molar, i.e. from 0.9 nM to 300 aM, compared to identical assays performed on glass plates), with spatial variation <9% [3]. The result is several orders of magnitude larger than the previous reported enhancement for the area-average and a single molecule at a hot spot, respectively. The D2PA substrate we proposed and demonstrated here is an array of 3D plasmonic nanocavity, which consists of a periodic non-metallic pillar array, metal disks and a metal back-plane on top and base of the pillars respectively, dense metallic nanodots on the pillar wall, and nanogaps between the metal components [1]. D2PA substrates were fabricated by nanoimprint, self-alignment, and self-assembly, which allows a fabrication of D2PA in a simple process and is well suited for mass production. In fabrication, SiO2 nanopillars were first patterned with nanoimprint and reactive ion etching (RIE), and then Au nanodisks, backplane and nanodots on the nanopillar sidewall were all formed within one step of Au evaporation. Finally, a thin layer of SiO2 was deposited on the Au surface conformally using plasma-enhanced chemical vapor deposition (PECVD) to avoid the quenching effect (i.e. signal losses caused by the coupling of the fluorescence emission to the nonradiant modes of the metal substrate). The ICG dye was deposited on D2PA by precise dropping [2]. And the Protein A was coated on D2PA by self-assembly through an adhesion layer [3]. Together with good spatial uniformity, wide dynamic range, and ease to manufacture, the giant enhancement in dye’s fluorescence, immunoassay’s fluorescence and detection sensitivity (orders of magnitude higher than previously reported) should open up broad applications in biology study, medical diagnosis, and others. [1] W. Li, F. Ding, J. Hu, and S. Y. Chou, Opt. Express, 19, 3925-3936 (2011) [2] W. Zhang, F. Ding, W. Li, Y. Wang, J. Hu and S. Y. Chou, Nanotechnology 23, 225301 (2012). [3] L. Zhou, F. Ding, H. Chen, W. Ding, W. Zhang, and S. Y. Chou, Analytical Chemistry, 84(10) 4489 (2012)

          8:00 PM - CC12.02

          Aerosol Manufacturing of Plasmonic Biosensors

          Georgios  A.  Sotiriou1, Christoph  O.  Blattmann1, Sotiris  E.  Pratsinis1.

          Show Abstract

          Aerosol synthesis of smart nanostructured materials is facile, efficient and scalable [1]. Incorporating this technique for manufacturing of nanoparticle devices will not only ensure excellent control over the nanoparticle morphology, but also facilitate the spread of nanoparticle technologies. Directly depositing silver nanoparticles synthesized by flame-spray-pyrolysis onto a substrate allows for a myriad of potential applications, in particular a biosensing device based upon the plasmonic properties of silver [2,3]. This project investigated silver nanoparticles [4,5], their corresponding directly deposited particle films and their potential as a biosensor. Silver on alumina support and the corresponding silica-coated counterparts were of primary interest. By tuning the process conditions, the silica coating thickness allowed for precise adjustment of the synthesized nanoparticles. The type of nanoparticles regulated the particle film morphology. Synthesizing and characterizing such particle films allowed to determine basic correlations attributed to the particles and their films. The particle’s suitability to function as a biosensor was investigated by conducting flow cell studies with relevant biomolecules. The biosensing was determined through the shift of the particle film characteristic extinction spectra. [1] S. E. Pratsinis, AIChE J. 2010, 56, 3028. [2] G. A. Sotiriou, S. E. Pratsinis, Curr. Opin. Chem. Eng. 2011, 1, 3. [3] G. A. Sotiriou, T. Sannomiya, A. Teleki, F. Krumeich, J. Vörös, S. E. Pratsinis, Adv. Funct. Mater. 2010, 20, 4250. [4] G. A. Sotiriou, S. E. Pratsinis, Environ. Sci. Technol. 2010, 44, 5649. [5] G. A. Sotiriou, A. M. Hirt, P. Y. Lozach, A. Teleki, F. Krumeich, S. E. Pratsinis, Chem. Mater. 2011, 23, 1985.

          8:00 PM - CC12.03

          Advancing Nanostructured Porous Si-based Optical Transducers for Label Free Bacteria Detection via ``Direct-cell-capture''

          Naama  Massad-Ivanir1, Giorgi  Shtenberg2, Ester  Segal1 3.

          Show Abstract

          In recent years, porous Si (PSi) has emerged as a promising nanomaterial for biosensing applications. This work demonstrates the use of PSi-based nanostructures as label-free optical biosensors for rapid bacteria detection (E. coli K12 as a model system). A key challenge in PSi biosensors is to effectively stabilize the nanostructure during experiments in biological solutions, as PSi oxidation and dissolution in aqueous environments lead to significant signal baseline drifts, signal loss, and ultimately to structural collapse of the PSi thin film. Another difficulty presented by PSi transducers is the susceptibility of proteins to undergo undesired conformation changes during deposition and patterning onto the Si. Thus, it was demonstrated that the use of PSi as template or as a host matrix may eliminate these issues, while providing the means for construction of complex optical structures from flexible materials, such as polymers. Specifically, the incorporation of hydrogels offers significant advantages due to their high optical transparency, good mechanical properties and ability to store and immobilize reactive functional groups. Two classes of label-free optical biosensors for bacteria detection are synthesized and characterized. The first platform is based on an oxidized PSi (PSiO2) nanostructure (Fabry-Pérot thin film) and the second consists of a PSiO2/hydrogel hybrid, in which polyacrylamide hydrogel is synthesized in situ within the nanostructured PSiO2 host. The different nanostructures' surfaces are biofunctionalized with specific monoclonal antibodies (IgGs), as a capture probe, and their potential applicability as a biosensor for bacteria detection is demonstrated. Exposure of these modified-surfaces to the target bacteria results in “direct-cell-capture” onto the biosensor surface. These specific binding events induce predictable changes in the thin-film optical interference spectrum of the biosensor. The sensing performance of the two different platforms, in terms of their stability in aqueous media and sensitivity, is compared and discussed. The hybrids show improved optical readout stability under aqueous conditions. Moreover, the presence of the hydrogel also enables desired conformation of the antibodies onto the biosensor surface during deposition and patterning, resulting in a higher sensitivity. This preliminary study suggests that biosensors based on PSiO2/hydrogel hybrid outperform the neat PSiO2 system. This proof-of-concept work demonstrates a simple and sensitive detection scheme of bacteria via a "direct-cell-capture" approach. Our preliminary biosensing experiments demonstrate a detection limit of 103-104 cells/mL for E. coli and a response time of several minutes.

          8:00 PM - CC12.04

          Plasmonic Biosensors Based on Synthetic Receptors

          Abdennour  Abbas1, Limei  Tian1, Jeremiah  J  Morrissey1, Evan  D  Kharasch1, Srikanth  Singamaneni1.

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          Recent progress in biomolecular imprinting has raised promising perspectives in replacing natural antibodies with artificial receptors. Significant efforts have been dedicated to the imprinting of organic and inorganic nanostructures, but very few were performed on nanomaterials with a transduction function. We describe a facile method for plasmonic hot spot-localized surface imprinting of gold nanorods using reversible template immobilization and siloxane co-polymerization. LSPR enables a fine control of the imprinting process at the nanometer scale and provides a nanobiosensor with high selectivity and reusability. As a proof of concept, we demonstrate highly sensitive and specific detection of neutrophil gelatinase-associated lipocalin (NGAL) biomarkers using localized surface plasmon resonance spectroscopy. The work reported here will be a valuable step towards plasmonic nanobiosensors with synthetic receptors for label-free and cost-efficient diagnostic assays. We expect that this novel class of surface imprinted plasmonic nanomaterials will open up new possibilities in advancing various biomedical applications of plasmonic nanostructures.

          8:00 PM - CC12.05

          Imaging Enhanced Spectral Upconversion from Rare-earth Doped Nanoparticles on Plasmonic Substrates

          Robert  Anderson1, Jon  Fisher1, Amy  Hor1, Paul  Stanley  May2, Mahdi  Baroughi3, Steve  Smith1.

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          We use spectroscopic imaging to investigate the enhancement of infra-red to visible upconversion in rare-earth doped nano-particles (NaYF4:Yb:Er) supported on nano-fabricated plasmonic substrates consisting of square lattices of Au nano-pillars fabricated by electron beam lithography and designed to support a surface plasmon polariton at frequencies which are near-resonant with the rare-earth ion (Yb3+) absorption [1,2]. We observe a systematic enhancement in the efficiency of upconversion associated with the interaction of the co-doped nano-particles with the plasmonic substrate. Spectrally-resolved imaging provides a massively parallel means of assessing the range of achievable enhancement and its relation to the specific configuration of the substrate / upconverting nano-particle system. Spectrally-resolved reflectivity of the plasmonic substrates confirms the role of the surface plasmon polariton in the upconversion enhancement. Experimental results are compared to Finite Difference Time Domain simulations of the frequency-dependent reflectivity of these nanostructures. [1] C. Lin, M. T. Berry, R. Anderson, S. Smith, and P. Stanley May, “Highly Luminescent NIR-to-Visible Upconversion Thin Films and Monoliths Requiring No High-Temperature Treatment,” Chem. of Materials 21 (14), 3406-3413 (2009). [2] H.P. Paudel, L. Zhong, K. Bayat, M.F. Baroughi, S. Smith, C. Lin, C. Jiang, M.T. Berry, and P.S. May, "Enhancement of Near-Infrared-to-Visible Upconversion Luminescence Using Engineered Plasmonic Gold Surfaces,” J. Phys. Chem C 115 (39), 19028-19036 (2011).

          8:00 PM - CC12.06

          Visible Mie Scattering of Hollow Silica Nanoparticles

          Markus  Retsch1 2, Marcus  Schmelzeisen3, Hans-Jürgen  Butt3, Edwin L.  Thomas2 4.

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          Colors in the visible range are known to be caused by light absorption for instance in organic dye molecules or by coherent light scattering of nanostructured materials such as opals. Furthermore, light scattering at small molecules causes the blue color of the sky or the complementary red horizon during sunset. Here we investigate another way of tuning colors over almost the entire visible spectral range, namely via Mie scattering. This incoherent light scattering method is possible by fabrication of monodisperse hollow silica nanoparticles (HSNP) with a shell as thin as 15 nm via a sacrificial templating method. Whereas the Mie resonance can be tuned by the particle diameter, the mean free path of light in such a HSNP powder is significantly enhanced by the low effective refractive index[1]. This effectively suppresses multiple light scattering and allows for a direct observation of distinct colors with the naked eye. Furthermore, we expand the investigation to hollow sphere with a thicker shell (up to 35 nm) and to shells made of titaniumdioxide to assess higher refractive index materials. [1] Retsch, M.; Schmelzeisen, M.; Butt, H.-J.; Thomas, E. L., Visible Mie Scattering in Nonabsorbing Hollow Sphere Powders. Nano Lett. 2011, 11, 1389-1394.

          8:00 PM - CC12.07

          Array-enhanced Plasmonic Nanoantennas for Multispectral Nanofocusing

          Jacob  Trevino1, Svetlana  Boriskina2, Bo  Yan4, Romain  Blanchard3, Federico  Capasso3, Bjoern  Reinhard4, Luca  Dal Negro5 1.

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          We report on the design and experimental demonstration of array-enhanced nanoantennas for polarization-controlled multispectral nanofocusing in the visible and near-IR spectral range. We design plasmonic dimer-gap nanoantennas coupled to multiple-periodic nanoparticle arrays to harvest light of designed wavelengths from a large spatial area and to focus it into a targeted nanoscale antenna feedgap. Analytical scattering and near-field calculations, based on Generalized Mie Theory, were performed on three dimensional (3D) Au nano-spheres to model the antenna coupling. Nanoantennas with wheel-like configurations were fabricated on glass substrates using electron beam lithography. Dark-field imaging and scattering spectroscopy are utilized to experimentally demonstrate polarization-dependent multispectral resonances enhanced by photonic-plasmonic coupling. Optical characterization of active nanoantennas using photoluminescence excitation (PLE) spectra will be presented to show multi-wavelength photonic coupling in agreement with theoretical antenna modeling. The nanoantenna presented yields the ability to focus optical energy into deep sub-wavelength areas and to address multiple spectral windows by polarization control. Such attributes are highly desired in biosensors, enhanced Raman scattering as well as nonlinear plasmonic applications.

          -

          CC12.08 Transferred to CC9.49

          Show Abstract

          8:00 PM - CC12.09

          Monitoring the Phase Transition in Nanoscale Polymer Films Using Plasmonic Nanostructures

          Limei  Tian1, Max  Fei1, Ramesh  Kattumenu1, Abdennour  Abbas1, Srikanth  Singamaneni1.

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          In this work, we demonstrate that plasmonic nanostructures can be employed as nanoscale transducers to monitor the growth and phase transitions in ultrathin polymer films. In particular, gold nanorods with high refractive index sensitivity (~150 nm/ refractive index unit (RIU)) were employed to probe the growth and swelling of polyelectrolyte multilayers (PEM). Atomic force microscopy was employed to reveal the uniform deposition of the PEM on gold nanorods. By comparing the wavelength shift and extinction intensity of the localized surface plasmon resonance (LSPR) of the gold nanorods coated with PEM in air and water, the swelling of PEM was estimated to be 26%±6%, which was confirmed with AFM imaging in air and water. The deployment of shape-controlled metal nanostructures with high refractive index sensitivity represents a novel and facile approach for monitoring the phase transition in polymers with nanoscale resolution.

          8:00 PM - CC12.10

          Biomimetic Plasmonic Paper-based SERS Substrate for Extremely Selective and Sensitive Explosive (TNT) Detection in Chemically Complex Media

          Saide  Zeynep  Nergiz1, Naveen  Gandra1, Limei  Tian1, Srikanth  Singamaneni1.

          Show Abstract

          Biomimetic material systems that demonstrate optimized and highly specific function synergized with optically active plasmonic nanostructures open path forward to unconventional nanosensor design and applications. In particular, such biomimetic approach has been applied to Surface Enhanced Raman Scattering (SERS) technique, that is a versatile analytical tool for trace-level biological and chemical detection, that impact homeland security, forensics, water and soil remediation, and nanomedicine. Current SERS substrates rely on improving the sensitivity owing to electromagnetic field enhancement localized in the vicinity of the surface of plasmonic nanostructures. However, non-specific interactions between analyte and plasmonic nanostructures often causes deterioration of electromagnetic field enhancement, and more importantly, lack of selectivity in challenging real world environments or conditions. Here we demonstrate a biomimetic approach to achieve extremely selective and sensitive plasmonic paper-based SERS substrate for TNT detection that comprised gold nanorods functionalized with TNT-binding peptide as molecular recognition element. Biomimetic plasmonic paper uptakes TNT in vapor, liquid or when swabbed over a contaminated surface with a detection limit of sub-nM, even in the presence of many other interfering chemicals and without any degradation in detection capabilities for several weeks. Biomimetic plasmonic nanosensors and devices could find applications in broad fields from homeland security, combinatorial biological and chemical sensing platforms to high-throughput point-of-care diagnostics and therapeutics.

          8:00 PM - CC12.11

          Optimization of Localized Surface Plasmon Resonance Transducers

          Ofer  Kedem1, Alexander  Vaskevich1, Israel  Rubinstein1.

          Show Abstract

          Nanostructured metal (e.g. gold, silver) surfaces exhibit an optical extinction band in the UV-to-NIR range, due to collective charge-density oscillations, termed localized surface plasmon resonance (LSPR). The intensity and energy of this band change in response to variation of the dielectric constant in the vicinity of the nanostructures (e.g., as a result of analyte binding), furnishing the basis for the use of such nanostructures as transducers in sensing applications. The performance of LSPR transducers is commonly quantified using the refractive index sensitivity (RIS), i.e., change in the resonance wavelength associated with unit change of the refractive index of the bulk medium. The transducer response to layer adsorption decays exponentially with the distance between the nanostructure and the adsorbed layer, due to the evanescently decaying electric field, extending from the nanostructure into the medium. The distance dependence of the LSPR response was investigated using random Au nano-island arrays fabricated by means of thermal deposition on glass slides followed by high-temperature annealing, coated with dielectric overlayers prepared by polyelectrolyte layer-by-layer adsorption. We found the decay length to be correlated with the nanoparticle size and the RIS.[1] The latter implies that optimization of the transducer response to a specific sensing application requires consideration of the dimensions of the recognition layer and the analyte. While the optical extinction can be monitored in either the transmission or reflection mode, we found that reflection measurements offer superior response.[2] [1] Kedem, O.; Tesler, A. B.; Vaskevich, A.; Rubinstein, I. Sensitivity and Optimization of Localized Surface Plasmon Resonance Transducers, ACS Nano 2011, 5, 748-760. [2] Kedem, O.; Vaskevich, A.; Rubinstein, I. Improved Sensitivity of Localized Surface Plasmon Resonance Transducers Using Reflection Measurements, J. Phys. Chem. Lett. 2011, 2, 1223-1226.

          8:00 PM - CC12.12

          Plasmonic Enhancement of Optical Absorption of UV Radiation in ZnO Thin Film Based Ultraviolet Photodetectors

          Akshta  Rajan1, Ayushi  Paliwal, Vinay  Gupta1, Monika  Tomar2.

          Show Abstract

          Surface Plasmon resonance or Plasmon propagating property in metal nanoparticles (NPs) has given a promising new approach to enhance the light trapping through absorption and scattering and then coupling light into the underlying optical modes of semiconductor surface. Surface Plasmon excitation in metal nanoparticles has been exploited and is of great interest in many applications like in photovoltaic devices, optical microscopy, molecular sensing and subwavelength photonics etc. Electromagnetic field enhancement due to plasmonic excitation which occurs in metal nanoparticles is of the great interest and is promising tool to increase the optical absorption and hence the photocurrent within the semiconductor. However, this efficient and interesting phenomena of plasmonics has not been explored much in the case of ZnO thin film based Ultra Violet (UV) photodetectors. In the present work, ZnO thin films have been fabricated by pulse laser deposition technique on platinum interdigital electrodes patterned on corning glass substrates under oxygen ambient at a deposition pressure of 100 mT. Small size NPs of silver (Ag), gold (Au) and Platinum (Pt) were synthesized using polyol synthesis technique and were spin coated on the top surface of ZnO thin films. Structural and optical properties of the ZnO thin films and metal NPs have been investigated using X-Ray diffraction (XRD), UV-Visible spectrophotometer and Transmission Electron Microscopy (TEM). Steady state photoresponse of all the prepared samples were investigated at 5 V bias by illuminating the samples using UV lamp (λ=365 nm, intensity=24 µwatt/cm2) as a radiation source. Photoresponse transients and data were taken using a Keithley 4200 SCS. XRD of ZnO thin film shows the growth of highly c-axis oriented thin film. Because of the formation of metal-semiconductor schottky junction for the metal NPs/ZnO photodetectors, a decrease in dark current was observed in comparison to that of pure ZnO thin film. An enhancement in current by about 4-5 orders in magnitude has been observed in the presence of UV rays for all the prepared samples. Photoconductive gain (K) for pure ZnO was found to be 3.1×103. Enhancement in K to 6.9×104, 5.3×104 and 5.0×105 with dispersal of Ag, Au and Pt NPs over ZnO thin film respectively were observed. The response characteristics have been studied in the light of two mechanisms. Firstly, the well established oxygen desorption and adsorption phenomena which is occurring in ZnO on interaction with UV radiation. Secondly, the plasmonic concept, according to which these small size metal NPs dispersed over ZnO thin film can be tuned to have sufficient absorption efficiency (Qabs) to absorb ultra violet photon energy and couple it with modes of ZnO leading to more no of electron hole pairs and hence the photocurrent. Improvement in rise and fall time was observed for Ag and Pt NPs coated ZnO thin film based UV photodetector which is necessary for detecting the UV rays.

          8:00 PM - CC12.13

          Non-monotonic Concentration Dependence of SERS Intensity in Trinitrotoluene (TNT) Detection: Mechanism, and Implications to Application

          Fei  Ding1, Eric  N.  Mills1, Weihua  Zhang1, Stephen  Y.  Chou1.

          Show Abstract

          Surface Enhanced Raman Scattering (SERS) has shown detection limits down to single molecule level, and uniform, repeatable performance using advanced nanostructured substrates (e.g. Klarite, and D2PA [1]). However, SERS signals often show non-linear, even non-monotonic, dependence on analyte concentration, posing challenges to practical sensing applications. To address this issue, we present a study of the non-monotonic concentration dependence of SERS intensity in detection of Trinitrotoluene (TNT) using Au D2PA substrates. A theoretical model is proposed, and verified using time-resolved and temperature-dependent experiments. This study will pave the way for SERS to become a reliable and quantitative analytical tool, not only for explosive detection, but also universally for many other analytes. In our experiments, SERS signals were collected from 3uL TNT acetonitrile solution, dropped and dried on 3mm×3mm D2PA substrates, in varying concentrations. It was found that at low concentrations (1pM to 1nM), the intensity of the 1360cm-1 peak (2,4,6-NO2 symmetric C-N stretch, in-plane mode) increases with concentration, while at intermediate concentrations (10nM to 10uM), signal intensity decreases. A sharp jump in intensity occurs around 100uM. The observed non-monotonic behavior can be interpreted by following model: (a) at low concentrations, molecules are well separated and show individual behavior, making in-plane modes Raman active when laser flipping the molecules sideways; (b) at intermediate concentrations, smaller inter-molecular distances cause larger inter-molecular forces, and the parallel orientation becomes harder to change, as a result the intensity of in-plane modes become weaker; and (c) at high concentrations, multiple layers are formed on the surface with multiple orientations, leading to an increase in both in-plane and out-of-plane modes intensity. To verify this model, we experimentally studied (1) the signal intensity evolution as a function of excitation time and (2) the signal intensity as a function of temperature at two different concentrations. In the first set of studies, focusing the laser beam on one spot, we found that the in-plane modes spontaneously appear, while out-of-plane modes vanish at longer excitation time. In the second set of studies, we found that SERS intensity of in-plane modes generally increase with temperature for a 1nM sample, while it remains unaffected by temperature for a 1uM sample. These experimental results confirm that the intensity changes are directly linked to re-orientations of TNT molecules, which can be driven by either laser or increased temperature, and prevented by energetic barriers imposed by intermolecular forces. With the understanding, this work shows the possibility towards practical applications with linear response by modifying surface properties and controlling measurement conditions. [1] W. Li, F. Ding, J. Hu, and S. Y. Chou, Opt. Express, 19, 3925-3936 (2011)

          8:00 PM - CC12.14

          Silver-decorated Cylindrical Nanopores: Combining the Third Dimension with Chemical Enhancement for Efficient Trace Chemical Detection with SERS

          Rajesh  Kodiyath1, Zachary  Allen  Combs1, Theodoros  A.  Papadopoulos2, Jian  Wang3, Hong  Li2, Richard  J. C.  Brown3, Jean-Luc  Bre.das2, Vladimir  V.  Tsukruk1.

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          We report on the facile fabrication of efficient porous alumina membrane-based SERS substrates that avoid the cumbersome stages of chemical surface modification of the pores and premixing/infiltration of nanoparticles with analytes. The design relies on higher light transmission through the SERS substrates by widening the cylindrical pore diameter to 355 nm and in situ growth of uniform silver nanoparticles on the inner walls. Electromagnetic simulations confirm that the interaction of excitation light with the nanoparticles along the pore walls can be maximized in such a membrane when the nanoparticles are placed within the first 14 µm of the pore depth. For common benchmark Raman analytes such as benzenethiol and Rhodamine 6G, nanomolar detection limits are readily obtained without any additional chemical surface functionalization and/or additional premixing and pre-concentration of metal nanoparticles and analytes. Moreover, a micromolar detection limit is achieved for the non-resonant, Raman-stealthy perchloric acid molecule. Quantum chemical calculations of perchloric acid bound to nanostructured silver clusters with different sizes and binding sites suggest that the maximum chemical enhancement is achieved for molecules located at the tips of the (111) planes of silver lattices, which are abundantly available on the nanoparticles grown in this study.

          8:00 PM - CC12.15

          SPR-Mediated Enhanced Functional Properties in Hybrid Nanostructures

          Dong Ha  Kim1, Yoon Hee  Jang1, Yu Jin  Jang1, Saji  Thomas  Kochuveedu1, Kyungwha  Chung1, Ji-Eun  Lee1, Li-Na  Quan1, Yonghwi  Kim2, Qingling  Xu1, Juyoung  Yoon1, Donghyun  Kim2, Jong Seung  Kim3.

          Show Abstract

          Surface plasmon resonance (SPR) phonemenon observed at noble metal nanostructures has been actively exploited in various fields of research themes. In this presentation, we introduce our recent efforts to develop functional nanoarchitectures employing tailor-designed plasmonic nanostructures toward potential applications in photovoltaics, photocatalysis, controlled light emission, and optical sensing. In the area of biosensing, an extremely simple SPR coupling-based setup is proposed via incorporation of metal NPs in a DNA sensing assay without any sophisticate and complicated design. In brief, biotin-streptavidin system was employed to immobilize probe DNA on basal Au substrates and three different types of models were designed employing Ag colloids or AuNPs with different size in different configurations. The sensitivity enhancement factor was compared experimentally using a Kretschmann configuration type SPR spectrometer. Concerning localized SPR based sensing, a SP-coupling-mediated sensor system is developed based on AuNPs tagged with a coordinative dipycolylamine and lipoyl-anchored naphthalimide derivative. The AuNPs with tailored ligands exhibit distinct sensing activity via sequential assembly into nanoparticle aggregates induced by metal ion complexing, and disassembly in the presence of pyrophosphate anions, which is accompanied by a swift, reversible color change due to a SPR coupling effect. Next, we discuss about the development of a surface plasmon induced visible light active photocatalyst system composed of titania nanoparticles decorated with Au nanoparticle arrays with different size and density distribution. TiO2 has been considered as most useful photocalyst for environmental remediation. Nevertheless, the large band gap of 3.2 eV restricts it use under UV light, which constitutes only 3% of the total solar spectrum. Here, we report SPR-induced visible light photocatalysis of TiO2/Au nanostructures having optimum configuration for the best photocatalytic efficiency. Plasmonic solar cells are also attracting tremendous attention as a means to enhance the performance of photovoltaic devices. Along the line of this subject, we show various strategies to increase the efficiency of plasmonic dye-sensitized solar cells by integrating hybrid plasmonic nanostructures including AuNPs with different size, core@shell NPs or NRs, Au/TiO2 configuration, etc., and discuss plausible mechanism for the efficiency enhancement. We also demonstrate that SPR can mediate and alter the photoluminescence property of a typical semiconductor nanostructure consisting of star-shaped ZnO decorated with AuNPs. In brief, the band emission of ZnO can be selectively enhanced via the transfer of defect emission from ZnO to Au based on the energy match between the defect emission of ZnO and SPR of Au NPs.

          8:00 PM - CC12.17

          Stable Magnetic Hot Spots for Simultaneous Concentration and Ultrasensitive SERS Detection of Solution Analytes

          Yongxing  Hu1, Yugang  Sun1.

          Show Abstract

          Fabrication of robust SERS substrates that can provide hot spots with reproducible SERS performance remains very attractive. Superparamagnetic, raspberry-shaped, mesoscopic gold particles (SRMGPs) with tunable optical properties can be fabricated via our special designed sol-gel approach and serve as ultra-active substrates for Surface-enhanced Raman scattering (SERS). The SRMGPs offers controllable hot spots in high density and are capable of enriching analyte molecules by the concentration effect induced by the superparamagnetic core. The excellent dispensability in aqueous solution and relative large surface area provide fully accessible hot spots by potential analyte, which facilitate the ultra low limit of detection till femto molar. Additionally, high reproducibility has been demonstrated. Our strategy for the synthesis of high SERS active SRMGPs offers great simplicity for the formation of effective SERS substrates for ultra sensitive detection.

          8:00 PM - CC12.18

          Holographically Patterned Nanotip Arrays with Controllable Morphological Features for SERS Applications

          Hwan Chul  Jeon1, Soojeong  Cho1, Seung-Man  Yang1.

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          Surface enhanced Raman scattering (SERS) is a powerful strategy for molecular sensing applications. Many studies have been developed for fabricating a large number of ‘hot-spots’ in SERS substrates and thereby achieving more enhanced Raman signals, which represent the spectral peaks of characteristic molecular structures. The sharp edges and nano-sized gap distances in metal nanostructures resulting in the enhancement of the local electromagnetic fields are important factors of SERS. However, sensitivity and reproducibility over a large area of such SERS substrates still remain crucial issues in spite of the recent advances in the design and fabrication of various SERS substrates. In this study, we demonstrate a facile method for the fabrication of hexagonally ordered nanotip arrays with controllable morphological features over large areas for SERS. Such periodic metallic nanostructures could be fabricated by using a combination of prism holographic lithography (HL), reactive ion etching (RIE), and e-beam evaporation. A He-Cd laser beam (325nm) and specially designed top-cut prism had been employed to achieve 2-layered face-centered cubic (FCC) structures of photoresist polymer which was used subsequently as templates. RIE using SF6 gas could control the features of polymeric template structures from triangular pyramid shaped- to conical shaped-nanotip arrays. Such nanotip arrays after directional Ag deposition procedure showed tunable SERS activities. Furthermore, additional O2 RIE formed the surface-roughness of resulting nanotip arrays. These controllable roughness of the nanotip arrays also resulted in the different SERS performance. Finally, the roughened region of the nanotip arrays showed a potential as a fluorescence-based sensing platform resulting from the increased adsorption capacity of target molecules caused by the enlarged surface area compared with smooth Ag film.

          8:00 PM - CC12.19

          Nanoengineering the Synthesis of Silica-gold Nanourchin Particles for Surface-enhanced Raman Spectroscopy

          Seung-Kon  Lee1, Victor  Sebastián Cabeza1, Klavs  F  Jensen1.

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          We report a novel method based on the combination of molecular self-assembly and reduction chemistry of gold species to synthesize gold nanowires densely grown on the silica nanoparticle with tailored surface morphology. The conjunction of several factors such as kinetically controlled crystallization of gold into nanowires and roughness of silica surface are determinants to obtain such novel nanostructures: silica-gold nanourchin (SGNU) particles. A continuous microfluidic reaction process was developed in order to assure better controllability and reproducibility on the growth of SGNUs. Raman spectroscopy results show large enhancement of surface-enhanced Raman scattering (SERS) from the substrates made from the assemblies of these SGNU particles.

          8:00 PM - CC12.20

          The Size and Edge Effects of Spin Crossover Nano-particles

          Azusa  Muraoka1, Kamel  Boukheddaden2, Jorge  Linares2, François  Varret2.

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          These theoretical investigations of the thermal and photo-switching properties of spin-crossover nanoparticles have shown at reproducing the collapse of the hysteresis effects at the critical size of the particles. In recent years, many research efforts have been devoted to the design of nanostructure of these magnetic materials in order to investigate the size reduction effects on their functionality and potential applications. Volatron et al. [1-3] suggested that spin crossover nanoparticles of Fe(pyrazine){Pt(CN)4} have well-controlled sizes and the critical size by the experimental investigation. The transmission electron microscope imaging (TEM) shows that reduction of the size results in the following effects, the transition temperature shifts downward and hysteresis loop is narrower and almost vanishes for the smaller particles, and residual high-spin fraction increases. We have analysed the size effect of spin-crossover transition nanoparticles by Monte Carlo study.[4] In this study, we focus on 2D core/shell model where the edge atoms are constrained to the high spin state on square and rectangular lattice of size. We perform Monte Carlo simulations based on the Metropolis algorithm using the Ising-like Hamiltonian. H = -J ∑(i,j)i=±1, j=±1S(i,j) S(i+i', j+j')+(Δ/2-Δ/kB/2 Ing)∑(i,j) S(i,j). Parameter values are chosen from typical data in spin-crossover literature, such as the molar entropy change ΔS ≈ 50 J/K mol leading to Ing = ΔS/R ≈ 6 (where R is the perfect gas constant) and energy gap Δ = 1300 K leading to a typical value of the equilibrium temperature Tequ = Δ/kBIng ≈ 200 K. Comparison to experimental values is possible through adequate energy rescaling, that is, by considering relative temperature variations. Simulations are performed on rectangular lattices (L×2L) of size. Changing the rectangle with side L upto 100, we found, (i) the width of hysteresis loop gradually increases and becomes size independent, (ii) the value of nHS (HS fraction) is reduced and the transition temperature increases and reaches the bulk value T1/2 = 2 Δ/kBIng in agreement with experimental observation. The rectangular particle size dependence introduced by HS fixed edges. The impact of specific conditions at the edges of the 2D model has been investigated. We predict to describe how the usual occurrence condition of the first-order transition has to be adapted to the nano scale. [1] F. Volatron et al., Inorg. Chem. 47, 6584 (2008) [2] L. Catala et al. Inorg. Chem. 48, 3360 (2009) [3] Y. Raza et al., Chem.Comm. 47, 11501 (2011) [4] A. Muraoka et al. Phys. Rev. B 84, 054119 (2011)

          -

          CC12.21 Transferred to CC2.08

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          Download Session Locator (.pdf)2012-11-30  

          Symposium CC

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          Symposium Organizers

          • Matthew Doty, University of Delaware
          • Srikanth Singamaneni, Washington University
          • Andrey L. Rogach, City University of Hong Kong
          • Mark Brongersma, Stanford University
          • Vladimir V. Tsukruk, Georgia Institute of Technology

            CC13: Surface Plasmons and Sensing

            • Chair: Srikanth Singamaneni
            • Friday AM, November 30, 2012
            • Hynes, Level 2, Room 208
             

            8:30 AM - CC13.01

            Electron Beam Lithographically Patterned Au Nanorods for High Temperature Plasmonic-based Gas Sensing

            Nick  Joy1, Michael  Carpenter1.

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            An optical sensing technique based on the surface plasmon resonance of Au nanoparticles embedded within a metal oxide thin film is being developed for harsh environment gas sensing applications where typical sensing devices readily fail. Previous work has shown stable and reliable sensing response to H2, CO, and NO2 at a temperature of 500°C for hundreds of hours. However, gas selectivity is still a challenge that needs to be addressed. From a materials approach, modification of the metal oxide chemistry or the Au nanoparticles may be advantageous in terms of influencing catalytic reactions or sensing response. The current work focusses on control over the Au geometry by using electron beam lithography to pattern arrays of Au nanorods which are then encapsulated in yttria stabilized zirconia (YSZ). The nanorod geometry is unique in that two localized surface plasmon resonant (LSPR) peaks result from electron oscillation along the transverse and longitudinal directions. In addition, the longitudinal LSPR peak position is tunable simply by changing the aspect ratio of the Au rods. This could potentially affect selective response based on an aspect ratio dependence to changes in the dielectric environment. Preliminary sensing results will be shown for several different aspect ratios along with some of the developmental issues in regards to patterning features on a quartz substrate and stabilizing the rod geometry at high temperature.

            8:45 AM - CC13.02

            Trace Level Vapor Detection of Explosive Related Organic Molecules by a SERS-active 3D Nanoporous Membrane Decorated with Silver Nanostructures

            Sidney  T.  Malak1, Rajesh  Kodiyath1, Zachary  A.  Combs1, Tobias  Koenig1, Mahmoud  A.  Mahmoud2, Mostafa  A.  El-Sayed2, Vladimir  V.  Tsukruk1.

            Show Abstract

            The combination of noble metal nanostructures and three dimensional metallic networks has led to the development of an effective SERS-active vapor detection platform. The adsorption behavior of silver nanocubes (AgNC) on the pore walls of porous alumina membranes (PAM) and their application toward vapor detection of important compounds found in many explosives has been investigated. The adsorption behavior of AgNCs coated with polyvinylpyrrolidone (PVP) was found to vary depending on the polyelectrolyte used to coat the PAM pore walls, allowing for a heterodispersed pattern of nanocube aggregates or a more evenly spaced pattern of individual nanocubes by using polyallylamine hydrochloride or polyethylenimine, respectively. Oxygen plasma etching was implemented before infiltration to allow for multiple AgNC loading cycles with minimal surface pore clogging. The high particle density over a large surface area lends itself to an increase in the overall SERS sensitivity for trace level detection through the wide-spread presence of accessible SERS hotspots. Therefore, trace vapor detection of the explosive stabilizing compound n-methyl-4-nitroaniline (MNA) was conducted and parts per billion concentrations were detected through the identification of three characteristic Raman peaks, demonstrating the effectiveness of this SERS platform for trace level vapor detection.

            9:00 AM - CC13.03

            Analysis of the Enhancement Variability in SERS with Nanoparticle-based Plasmonic Substrates

            Oded  Rabin1.

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            Surface enhanced Raman spectroscopy (SERS), an analytical technique with high sensitivity and high chemical differentiation power, relies on the strong localization of electric fields by surface plasmons. The electric field distribution around nanostructures depends, in turn, on the nanoscale geometry of the surface and the spatial variation of the dielectric function. Small changes in this local electric field result in large changes in Raman scattering signals. Due to process variations in the mass fabrication of plasmonic nanostructures, SERS repeatability is non-trivial. Synthesis of monodisperse silver nanocubes and templated self-assembly of the nanoparticles into small clusters were used to generate hundreds of microscopic SERS substrates with useful attributes to demonstrate the relationship between structure and plasmonic properties. A strong link between SERS enhancement, number of nanoparticles in a cluster, cluster orientation and relative alignment between particles in a cluster is established. Lower variability in SERS enhancements was achieved by controlling only a few of the geometric parameters of the clusters, within the tolerances of conventional nano/micro- fabrication processes. In clusters of silver nanocubes, while previous work predicted a higher SERS enhancement with nanocubes aligned face-to-face, our experiments repeatedly show that edge-to-face junctions produce higher substrate enhancements. Furthermore, through the analysis of experimental and computational results from a large set of cluster geometries, a strong case was made for the central role surface plasmon resonances have in mediating between the nanoparticle geometry and the far-field spectroscopy; i.e. matching the laser frequency and the localized plasmon resonance frequency is a key step in optimizing SERS.

            9:15 AM - CC13.04

            Enhanced Photoluminescence in Plasmonic Resonant Nanocavities

            Keiko  Munechika1, Mihail  Bora1, Elaine  M  Behymer1, Dietrich  Dehlinger1, Jerald  Britten1, Cindy  C  Larson1, Allan  SP  Chang1, Hoang  T  Nguyen1, Tiziana  Bond1.

            Show Abstract

            We study the photoluminescence enhancement of dyes using plasmonic resonant cavities composed of vertical silver nano-wires. Plasmon resonance occurs when the length of the cavity is an odd multiple of quarter plasmon wavelength. Photoluminescence is enhanced by increasing both absorption and emission of the dyes by designing a cavity that has two resonances that are aligned with dye extinction and emission. Absorbance of the dye inside the cavity is increased due to the high localized electromagnetic energy density accounting for more efficient excitation that is proportional to the square of the electric field (E2). Emission is also increased by an E2 factor due to more efficient coupling of dipole emission into the radiative modes. Photoluminescence spectrum and decay lifetime of the dyes within the 50-100nm wide cavities are measured as the plasmon resonance frequency is tuned near absorption and/or emission. We discuss how plasmon resonances correlate with reduction in lifetime, increase in emission intensity and change in the photoluminescence spectrum. Our experimental results will be related to numerical simulations which predict a localized electric field enhancement of ~12 suggesting more than four orders of magnitude photoluminescence enhancement limit. We conclude with pointers for increasing the field enhancement and potential realization of a sub-wavelength plasmon laser. Prepared by LLNL under Contract DE-AC52-07NA27344.

            9:30 AM - *CC13.05

            Plasmonically Sensitized Photoprocesses

            Martin  Moskovits1, Syed  Mubeen2.

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            Titania, has a bandgap of ~3.2 eV and therefore absorbs strongly only in the UV. However, devices fabricated with (nonpercolating) multilayers of AuNPs in a TiO2 film can be fabricated which when illuminated at 600 nm produced over 1000-fold increase in photoconductance over what TiO2 films devoid of AuNPs produce. The overall current resulting from illumination with visible light is ~50% of the device current measured with UV illumination. We ascribe this to the direct injection by quantum tunneling of hot electrons produced in the decay of localized surface-plasmon polaritons excited in gold nanoparticles (AuNPs) embedded in the semiconductor. The electronic properties of the device measured alternately in the dark and when illuminated support this picture.

            10:00 AM -

            Break

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            10:30 AM - *CC13.06

            Plasmonics with Gold Nanobelts

            Jason  H.  Hafner1 2, Lindsey  J. E.  Anderson1, Courtney  M.  Payne2, Michael  F.  Reynolds3.

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            Gold nanobelts are chemically synthesized plasmonic nanowires with sub-100 nm rectangular cross sections and lengths greater than 10 microns. They exhibit a strong scattering plasmonic mode that is tunable with cross-sectional aspect ratio, yielding nanobelts of different colors in dark field microscopy. Several nanobelt structures and potential applications will be discussed. Uniformly tapered gold nanobelts have a spatially varying plasmon resonance that has been used to image the spectral plasmonic enhancement of nearby quantum dots. Nanobelts occasionally split during their growth, leaving two nanobelts with a uniform sub 10 nm gap that may be an ideal substrate for analytical surface enhanced Raman spectroscopy. Plasmon propagation has been detected in gold nanobelts at visible and near infrared wavelengths. The specific modes that support propagation have been identified and studied. Finally, individual gold nanobelts have been attached to probe tips to evaluate their mechanical properties and performance as atomic force microscopy tips. The nanobelts exhibit elastic buckling behavior and are sufficiently robust for tapping mode imaging. Their sharp scattering plasmon resonance and gold surface chemistry may make them highly versatile near field probe tips.

            11:00 AM - CC13.07

            The Origin of Oscillations in the Long-range Response of Localized Surface Plasmon Resonance Transducers

            Ofer  Kedem1, Takumi  Sannomiya2, Alexander  Vaskevich1, Israel  Rubinstein1.

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            Layered plasmonic/dielectric systems exhibit interaction of collective charge density oscillations in the plasmonic layer (typically metallic nanostructures) with the dielectric overlayer. The nature of the interaction affects the intensity and energy of the localized surface plasmon resonance (LSPR), the latter seen as an extinction band in the UV-to-NIR range. The transducer response to a dielectric overlayer is based on the interaction of the layer with the plasmon evanescent electric field, extending from the nanostructures into the medium; the response decays exponentially with the distance between the metal nanostructures and an adsorbed layer.[1] Recently, several groups reported response to dielectric layer adsorption at distances far greater (hundreds of nanometers) than previously seen, beyond the known plasmon decay length (typically few to tens of nanometers). This was termed “long-range LSPR response”, and its use in sensing applications was suggested. Several attempts were made to explain the effect, though none was satisfactory. Using random Au nano-island arrays of several average particle sizes, fabricated by means of vapor deposition on glass slides followed by high-temperature annealing, we found the oscillations to be independent of the particle size.[2] The oscillations were reproduced using computational models, and were found to be the result of interference effects, modulating the energy distribution between absorption, transmission and scattering modes. Two-dimensional data analysis allowed us to extract the phase shift at the nanoparticle interface. [1] Kedem, O.; Tesler, A. B.; Vaskevich, A.; Rubinstein, I. Sensitivity and Optimization of Localized Surface Plasmon Resonance Transducers, ACS Nano 2011, 5, 748-760. [2] Kedem, O.; Sannomiya, T.; Vaskevich, A.; Rubinstein, I. The Origin of Oscillations in the Long-Range Response of Localized Surface Plasmon Resonance Transducers, submitted.

            11:15 AM - CC13.08

            Gold Nanorods: Influence of Tip Face Morphology on Plasmonic Sensing

            Tobias  AF  Konig1, Maneesh  K  Gupta1, Vladimir  V  Tsukruk1.

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            Significant progress has been achieved in the field of plasmonics of complex nanostructures, but observation of localized surface plasmon resonances (LSPR) at a length scale of a few nanometers is still a challenge. In the case of contact limit between two nanoparticles, the influence of particle shape is rarely discussed. Two challenges still remain: The ability to precisely fabricate large numbers of monodisperse aggregates and the precise characterization of the local enhanced field. Template-assisted fabrication techniques present one route to address this challenge allowing for high-throughput synthesis of nanorod arrays with precise control of rod length and spacing between auxiliary aligned rods for high locally enhanced surface plasmon resonances. However, template-assisted technique typically yields nanorods with rough non-flat ends (usually a concave or convex crescent shape) that can dramatically alter the optical properties. In this work, we conduct FDTD simulation of the influence of the tip face shape of gold nanorod monomers/dimers and compare it with single particle LSPR spectra obtained from dark field optical microscopy. The inclusion of specific tip shapes provides understanding for plasmonic properties of non-trivial face ends. Understanding the close convex-concave contact between nanorods will be important to improve the sensitivity of LSPR sensors.

            11:30 AM - CC13.09

            Hybrid Plasmonic-photonic Substrates for on-chip Sensing and Spectroscopy

            Maysamreza  Chamanzar1, Siva  Yegnanarayanan1, Zixuan  Xia1, Ehsan  Shah Hosseini1, Ali  Adibi1.

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            We have shown the implementation of novel hybrid plasmonic-photonic integrated devices for efficient on-chip sensing and spectroscopy. Plasmonic nanoresonators have localized surface plasmon resonances (LSPR) that exhibit ultra-high field enhancements. They have been used for LSPR sensing with very large sensitivities, and also surface enhanced Raman spectroscopy (SERS). Photonic waveguides and whispering gallery resonators can guide and trap light on the chip with ultra low losses. We have shown that if plasmonic nanoresonators are integrated with waveguides and on-chip whispering gallery resonators, both advantages of integrated photonics and plasmonic structures can be combined in a unified platform enabling new potentials for on-chip sensing and spectroscopy. The proposed hybrid plasmonic-photonic structures consist of waveguide-based devices for LSPR sensing, and resonator-based devices for on-chip SERS. In the proposed waveguide-based structures, the LSPR mode of individual gold nanorods can be excited with efficiencies exceeding 10% in a broad bandwidth covering the entire resonance linewidth of the gold nanorods. We have demonstrated large sensitivities (~200 nm/RIU) for gold nanorods integrated on Silicon Nitride (SiN) waveguides. We have also shown that by integrating a single gold nanoparticle with a SiN microring resonator, the field enhancement in the microring whispering gallery resonance modes can be combined with the field enhancement in the plasmonic nanoresonators to achieve ultra-high SERS enhancements. Using such a double resonator structure with a 15um-radius microring resonator, it is possible to couple about 80% of the input light to the localized modes of 100nm×40nm×30nm gold nanorods, and therefore an additional 900 fold Raman enhancement (~3 orders of magnitude improvement) is possible. In this paper, we demonstrate our latest sensing results using the proposed hybrid plasmonic-photonic structures. We will experimentally show the integration of microfluidic channels with the hybrid substrate as a fully functional sensing platform. The proposed unconventional substrates are alignment-insensitive, since the plasmonic nanoparticles are lithographically fabricated at their optimal locations, and once light is coupled to the on-chip bus waveguides, the LSPR modes of plasmonic nanoparticles are excited. We will discuss the design as well as the fabrication and characterization of these structures. The fabrication involves two steps of electron beam lithography (EBL) to define photonic and plasmonic structures. The photonic guided-wave structures are realized by inductive-coupled-plasma (ICP) etching of the SiN film, and the plasmonic nanoparticles are realized by metal evaporation and lift-off. The characterization is done using a supercontinuum broadband laser source covering a wavelength range of 500-1800nm. We will demonstrate sensing of different analytes at different concentrations using the proposed structures.

            11:45 AM - CC13.10

            Graphene-enabled Silver Nanoantenna Sensors

            Jason  C  Reed1, Hai  Zhu1, Alexander  Yutong  Zhu1, Ertugrul  Cubukcu1.

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            Silver is the ideal material for plasmonics because of its low loss at optical frequencies, but is often replaced by a more lossy metal, gold. This is because of silver’s tendency to tarnish and roughen, forming Ag2S on its surface, dramatically diminishing optical properties and rendering it unreliable for applications. This occurs because of the chemical reaction of the silver surface to hydrogen sulfide (H2S) and carbonyl sulfide (OCS) in ambient air. Graphene has been found to be an impervious membrane, unable to be penetrated by atoms as small as helium. By passivating the surface of silver nanostructures with monolayer graphene, these atmospheric sulfur containing compounds are unable to penetrate the graphene to degrade the surface of the silver. Preventing this sulfidation eliminates the increased material damping and scattering losses originating from the unintentional Ag2S layer. Because it is atomically thin, graphene does not interfere with the ability of localized surface plasmons to interact with the environment in sensing applications. Furthermore, after 30 days, graphene-passivated silver nanoantennas exhibit 27-times higher sensitivity over that of bare Ag nanoantennas, and two orders of magnitude improvement in peak width endurance. We compare these experimental results with finite-difference time-domain (FDTD) simulations as well as calculations using quasistatic Mie theory. By employing graphene in this manner, the excellent optical properties of silver can be functionally utilized in a variety of nanoscale plasmonic devices and applications.

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