KK7: Quantum Plasmonics & Metamaterials
Chair: Vassilios Kovanis
- Thursday AM, April 12, 2012
- Moscone West, Level 3, Room 3003
8:30 AM - *KK7.1
Nonlocal Plasmonics and Nonlinear Optical Metamaterials
Center for Metamaterials and Integrated Plasmonics, Duke University, Durham, North Carolina, USA; 2,
C.M. Bowden Research Facility, US Army, RDECOM, Redstone Arsenal, Alabama, USA.Show Abstract
Metamaterials have provided new and interesting linear media that have provided a venue to explore otherwise inaccessible concepts1. Analogously, nonlinear metamaterials based on metals are appealing for potential use in nonlinear optical applications at infrared or visible wavelengths. Plasmonic field enhancement, along with the intrinsic nonlinearity of metals, makes metal-based nonlinear optical metamaterials a concrete possibility. In particular, we investigate second order nonlinear phenomena. Although metals are centrosymmetric and do not possess an inherent Ï‡(2) nonlinearity, the surface of a metal can break the symmetry and provide a mechanism for an effective Ï‡(2) nonlinearity. This homogenizedÏ‡(2) nonlinear response thus becomes highly dependent on the metal geometry, making it inherently a metamaterial construct. Moreover, the origin of nonlinearity in metals arises from both volume and surface contributions. Nonlinear surface contributions are strictly related to the response of the electrons within a Fermi wavelength (~5Ã…) from the metal boundaries. In this sub-nanometer realm, electron-electron interactions become non-negligible and non-local effects must be taken into account. We present an analysis of second-harmonic generation in plasmonic systems of arbitrary shape2. The nonlinear optical response of the metal is described by a hydrodynamic model, which includes the effects of quantum pressure associated with the electron gas3. In particular, plasmonic systems are investigated, in which metal nano-structures are strongly coupled to a metal film. As the gap region reaches distances of fractions of a nanometer, non-local effects become predominant and a saturation of the electric field enhancement occurs. The nonlinear effects are thus intrinsically connected to the linear non-local properties of the system. The free electron limit, in which the pressure is completely neglected, is also investigated. In this limit nonlinear surface contributions are expressed in terms of the polarization vector in the bulk regions2, thus avoiding tackling more complex, 3D equations. We then numerically investigate second-harmonic generation arising from U-shaped metal nanoparticles and show that its basic characteristics may be explained solely by the electric properties of the structure rather then its magnetic response, in contrast to previous works4. References 1J. B. Pendry, D. Schurig, and D. R. Smith, â€œControlling Electromagnetic Fields,â€ Science 312, 1780â€“1782 (2006). 2C. CiracÃ¬, E. Poutrina, M. Scalora, and D. R. Smith, â€œSecond-Harmonic Generation in Plasmonic Metamaterialsâ€, submitted. 3M. Scalora, M. A. Vincenti, D. de Ceglia, V. Roppo, M. Centini, N. Akozbek, and M. J. Bloemer, â€œSecond- and third-harmonic generation in metal-based structures,â€ Phys. Rev. A 82, 043828 (2010). 4 M. W. Klein, C. Enkrich, M. Wegener, and S. Linden, "Second-harmonic generation from magnetic metamaterials," Science 313, 502â€“504 (2006).
9:00 AM - KK7.2
Reversing the Size-dependence of Surface Plasmon Resonances: Surface Chemistry Matters
Center for Nanoscale Materials, Argonne Nat Lab, Argonne, Illinois, USA.Show Abstract
Surface chemistry can become pronounced in determining the optical properties of colloidal metal nanoparticles as the nanoparticles become so small (diameters <20 nm) that the surface atoms, which can undergo chemical interactions with the environment, represent a significant fraction of the total number of atoms although this effect is often ignored. For instance, formation of chemical bonds between surface atoms of small metal nanoparticles and capping molecules that help stabilize the nanoparticles can reduce the density of conduction band electrons (i.e., free electrons) in the surface layer of metal atoms. This reduced electron density consequently influences the frequency-dependent dielectric constant of the metal atoms in the surface layer and, for sufficiently high surface to volume ratios, the overall surface plasmon resonance (SPR) absorption spectrum. The important role of surface chemistry will be discussed by carefully analyzing the classical Mie theory and a multi-layer model will be presented to produce more accurate predictions by considering the chemically reduced density of conduction band electrons in the outer shell of metal atoms in nanoparticles. Calculated absorption spectra of small Ag nanoparticles quantitatively agree with the experimental results for our monodispersed Ag nanoparticles synthesized via a well-defined chemical reduction process, revealing an exceptional size-dependence of absorption peak positions: as particle size decreases from 20 nm the peaks blue-shifts but then turns over near ~12 nm and strongly red-shifts. A comprehensive understanding of the relationship between surface chemistry and optical properties will be beneficial to exploit new applications of small colloidal metal nanoparticles, such as colorimetric sensing, electrochromic devices, and surface enhanced spectroscopies. Use of the Center for Nanoscale Materials was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
9:15 AM - KK7.3
Quantum Plasmon Resonances of Individual and Coupled Metallic Nanoparticles
Scholl1, Ai Leen
Materials Science and Engineering, Stanford University, Stanford, California, USA; 2,
Stanford Nanocharacterization Laboratory, Stanford University, Stanford, California, USA.Show Abstract
The plasmon resonances of individual and coupled metallic nanoparticles have received considerable attention for their applications in nanophotonics, biology, sensing, spectroscopy, and solar energy harvesting. While individual spheres larger than 10 nanometers and dimers with gaps greater than 1-2 nm have been thoroughly characterized, their properties at smaller sizes (entering the quantum regime) have been historically difficult to describe. Quantum-sized individual plasmonic particles exhibit very low extinction cross-sections while closely-spaced colloidally-synthesized dimers have been challenging to control. Such difficulties preclude experimental analysis of quantum-plasmonic systems, which are highly relevant to many natural and engineered processes. In this presentation, we investigate the plasmon resonances of individual ligand-free silver nanoparticles using aberration-corrected transmission electron microscope (TEM) imaging and monochromated scanning TEM electron energy-loss spectroscopy (STEM EELS). This technique allows direct correlation between a particle's geometry and its plasmon resonance. As the nanoparticle diameter decreases from 20 nm to less than 2 nm, the plasmon resonance exhibits a blue-shift from 3.3 eV to 3.8 eV, with particles smaller than 10 nm showing a substantial deviation from classical predictions. We present an analytical quantum-mechanical model that well describes the plasmon resonance shift due to a change in particle permittivity. Our results highlight the unique quantum plasmonic properties of small metallic nanospheres, with direct application to understanding and exploiting catalytically-active and biologically-relevant nanoparticles. Furthermore, using TEM EELS, we can observe the plasmonic properties of multi-particle systems. Using excitation from the electron beam, ligand-free silver particles are capable of moving on silicon nitride substrates, allowing dynamic monitoring of plasmonic resonances as the particles approach each other and coalesce. This strategy provides a straightforward method for studying dimer interactions at variable separation distances, including quantum-sized separations. Because individual sets of particles can simultaneously imaged and spectrally analyzed, we can directly probe the crossover from classical to quantum plasmon resonances in particle dimers.
9:30 AM - KK7.4
Plasmon Resonances in Atomic-scale Gaps
Experimental Physics 5, University of Wuerzburg, Wuerzburg, Germany; 2,
Technical Physics, University of Wuerzburg, Wuerzburg, Germany; 3,
Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan; 4,
Dipartimento di Fisica, Politecnico di Milano, Milano, Italy.Show Abstract
The great asset of plasmonic systems is their ability to concentrate and enhance electromagnetic fields in nanometer sized dimensions. The increase in light-matter interactions associated with the highly confined fields is of great importance for sensing , quantum and non-linear optics. Structures with gaps are of particular interest because in these systems the opposite charge accumulation on both sides of the gap can lead to very high electric fields. We experimentally investigate the plasmon resonances of side-by-side aligned single-crystalline gold nanorod dimers. Robust gaps between the particles reaching well below 1 nm are formed by reproducible self-assembly. For such atomic-scale gaps extreme splitting of the symmetric and anti-symmetric dimer eigenmodes is observed in white-light scattering experiments. Besides providing evidence for atomic-scale gap modes at visible wavelengths with correspondingly small mode volumes, our experimental results can serve as a benchmark for electromagnetic modeling beyond local Maxwell theory [1, 2]. References:  GarcÃa de Abajo F.J. J. Phys. Chem. C, 112, 17983-17987 (2008)  Zuloaga, J.; Prodan, E.; Nordlander, P. Nano Lett. 9, 887-891 (2009)
9:45 AM - KK7.5
Towards Quantum Coherent Metamaterials
Applied Physics and Materials Science, California Institute of Technology, Pasadena, California, USA.Show Abstract
During last twenty years the field of nanophotonics and metamaterials has advanced dramatically. Up to the recent times, metamaterials have been considered as classical electromagnetic structures, and the research has been mainly focused on classical aspects of light-metamaterial interactions. However, interesting phenomena stem from the quantum nature of interaction of nanostructures and light. We report here a theoretical investigation of the cooperative behavior of quantum emitters embedded in nanostructured materials. In the recent years, the interest in the Dicke model  has been revived since it is a simple model system in which one can find multi-partite entanglement. Inspired by the Dicke model, we first address collective spontaneous emission process of a dense ensemble of radiating two-level quantum objects embedded in a metamaterial. The radiative coupling between quantum emitters causes the emergence of collective modes whose lifetimes are longer or shorter compared to those of uncorrelated independent quantum emitters. Whereas in the original Dicke model of quantum emitters in free space spontaneous emission takes place in a timescale inversely proportional to the number of radiating atoms N and the emission intensity is proportional to N squared, in our case we observe a modified power-law dependence of the emission timescale and intensity. We also show that the collective damping parameter is an oscillatory function of inter-emitter spacing. Further, we analyze the dynamics of the ensemble of the two-level emitters under continuous pumping. For the both cases we derive analytical expression for the electric field operator in the far field and calculate first- and second-order correlation functions of the emitted light. This enables us to define physically measurable quantities such as the emission spectrum and intensity of the emitted light. We also analyze photon statistics and nonclassical properties of the radiation field. From the analysis of long-range coupling, we derive conditions for the superradiance, which may play a significant role for ultrafast applications. Interestingly, the proposed system allows for post fabrication tuning of the emission properties of the metamaterial. We will discuss routes to modified emission, e.g., by applying external electric fields that can dynamically modify the transition energy of the quantum emitters via an induced Stark shift. References  R.H. Dicke, Phys. Rev. 93, 99 (1954).
10:00 AM -
KK11: Poster Session
Chair: Jennifer Dionne
- Thursday PM, April 12, 2012
- Marriott, Yerba Buena, Salons 8-9
8:00 PM - KK11.1
Investigation on the Relationship between Internal Coupling Effects and Zero Refractive Index in a Metallodielectric Composite
Li1 2, Helen
Applied Physics, The Hong Kong Polytechnic University, Hong Kong SAR, China; 2,
, Shenzhen Graduate School of Tsinghua University, Shenzhen, China.Show Abstract
Zero refractive index materials are materials where light can propagate without phase delay. In this paper, the relationships between internal coupling effects and zero refractive index in a metallodielectric composite are studied in detail. The proposed composite is made of metal pieces and spiral wires periodically arranged in an epoxy dielectric matrix. Full wave simulation was performed to obtain the dispersion relationship (refractive index versus frequency) and field distributions of the structure. Near zero refractive index is observed at the range between 2~3GHz. In this range, as shown by the field distribution graph, negative electric/magnetic polarizations are induced by currents and charges vibrating out-of-phase with incident EM waves. By careful analysis of the dispersion curve, it is found that the bandwidth can be significantly enhanced when adjacent metallic elements are coupled transversely rather than longitudinally, while frequency (at which n=0) is easily to be shifted by adjusting lengths and curvatures of spiral wires. Based on these results, the structure was applied as a zero index superstrate over a patch antenna, whose directivity is subsequently improved by 14 times. It is also indicated that the structure can be scaled down into micrometers for Terahertz uses.
8:00 PM - KK11.2
Enhanced Thermal Stability of Plasmonic Gold Nanorods by Silica-coating and Their Application to Thin Film Photovoltaics
Materials Science Program, University of Rochester, Rochester, New York, USA; 2,
Department of Chemistry, University of Rochester, Rochester, New York, USA.Show Abstract
Gold nanoparticles have good localized surface plasmon resonance (LSPR) in the visible and near-infrared region of spectrum, which offering them potential applications to optoelectronics. Those LSPR can be finely tuned by the nanostrucutres with controllable sizes and shapes. Gold nanorods with controllable LSPR can be easily achieved by synthesizing nanorods with different aspect ratio. However, the structure gold nanorods with large surface-to-volume ratio are not stable and will reshape to from nanospheres at high temperature due to minimization of surface free energy. It is believed that gold nanorods cannot survive after annealing at 250 degree Celsius for 30 minutes. This low thermal stability of gold nanorods may not be compatible with high temperature characteristics of semiconductor processing and limit their applications. Here, we report that the thermal stability of gold nanorods can be greatly enhanced by silica-coating. After thermal annealing at 600 degree Celsius for 1 hr, silica-coated gold nanorods still remain their rod structure with minor transformation into shorter and thicker rods. In comparison, bare gold nanorods all turn into gold nanospheres after thermal annealing. The spectral data also confirm the structural changes observed by scanning electron microscope. We also report the recent progress in application of plasmonic gold nanorods to thin film photovoltaics to improve absorption through scattering and electromagnetic field localization effects.
8:00 PM - KK11.3
Highly Sensitive Surface-enhanced Raman Scattering Substrate Based on Ag Coated Monodispersive Silica Colloid Monolayer
Department of Materials Science and Engineering, National Taiwan University, Taipei City, Taiwan; 2,
Institute of Polymer Science and Engineering, National Taiwan University, Taipei City, Taiwan; 3,
Department of Physics, National Taiwan University, Taipei City, Taiwan.Show Abstract
The fabrication of periodic metallic structure has gained many interests due to its surface plasmon resonance behavior in recently years. By coupling a radiation dipole with a surface plasmon generated on the surface of noble metals, energy can transfer effectively from the dipole into the surface plasmon resonance. Localized surface plasmon resonance is strongly dependent on the size, shape, surrounding environment and metal features. In this study, we develop a simple and low cost solution process to fabricate a novel Ag coated monodispersive silica colloid monolayer substrate to enhance Raman scattering signals of various organic dyes. For SERS substrate fabrication process, we first synthesized amorphous monodispersive spherical silica particles by using the sol-gel method. Tetraethylorthosilicate (TEOS) was dissolved in ethanol and the solution was held and stirred with a mechanical stirrer in water bath at 30 Â°C for 30 min. Then ammonia solution was added into the TEOS solution and stirred for 2 h. After 2 h of reaction, a monodispersive silica colloid solution was obtained. Next, we changed the parameters, such as the concentration of monodispersive silica colloid solution, solvent type, spin-coating speed, to obtain the optimal monodispersive silica colloid monolayer. After monodispersive silica colloid was self-assembled on the silicon wafer, Ag was deposited on the silica monolayer by thermal evaporation to obtain Ag coated silica monolayer. The surface morphology of SERS substrate was studied by atomic force microscopy and scanning electron microscopy; the extinction spectra was measured by using a spectral micro-reflectometer equipped with an optical microscope. In order to confirm the effect of surface-enhanced Raman scattering of organic compounds on the SERS substrate, methyl red, methyl orange and methylene blue were used as model compounds. The compound was spin coated on the SERS substrate and evaluated its Raman scattering respectively. A large enhancement of Raman scattering was observed when the SERS and SPR were correlated in the surface morphology of the SERS substrate at the exciting wavelength of 632.8 nm. The optimal SERS substrate shows the largest Raman scattering signal enhancement of up to 44,500 times. This study provides a simple process to fabricate highly sensitive SERS substrate that can enhance the intensity of Raman spectrum of organic compound by tuning process parameter easily. The observed SERS in this study will be beneficial for the design and fabrication of functional devices and sensors.
8:00 PM - KK11.4
Influence of Metal Nanoparticles Embedded in a Buffer Layer of Organic Photovoltaics on Plasmonic Absorption Enhancement
Kim1, Taek Seong
Lee1, Doo Seok
Jeong1, Wook Seong
Electronic Materials Research Center, Korea Institute of Science and Technology, Seoul, Republic of Korea.Show Abstract
The effects of Au or Ag nanoparticles on optical absorption enhancement of organic photovoltaics based on blended poly(3-hexylthiophene):phyenyl-C61-butylric acid methyl ester (P3HT:PCBM) were investigated using a finite-difference-time-domain (FDTD) method. The various shaped nanoparticles such as sphere, plate and semi-spheroid were chosen in this study. First, the spherical metal nanoparticles were embedded in a buffer layer of 20 nm thickness and their size was varied from 10 nm to 50 nm. The metal nanoparticles with 10 ~ 20 nm diameter offered negligible absorption enhancement in an active layer. Unlike those short metal nanoparticles, the incorporation of the taller metal nanoparticles than the buffer layer led to a significant absorption enhancement by plasmonic resonance especially in case of Ag nanoparticles. Ag nanoparticles gave broader and stronger absorption enhancement in the active layer than Au nanoparticles. 34 % enhancement in the optical absorption of the active layer was observed with Ag nanoparticles with 50 nm diameter at 10 % coverage. The electric field distributions around spherical metal nanoparticles, their self-absorption, and the active layer thickness dependence on the absorption enhancement were also discussed. Second, the influence of Ag nanoparticles of plate/spheroid shape on optical absorption of the active layer was studied. Nanoplates of disc, square, triangular plate and oblate semi-spheroid shape were embedded in the buffer layer, and their height was set for 20 nm of the same thickness as the buffer layer. Embedding Ag nanoplates of optimal lateral dimension in the buffer layer provided substantial optical enhancement in the active layer. The resonance wavelength of metal nanoplates was able to be tuned by adjusting their lateral dimension, which was one of the keys to enhancing optical absorption of the active layer.
8:00 PM - KK11.5
Silver and Gold Nanocubes as Active Substrates for the SERS Detection of Organochloride Compounds
, University of São Paulo, São Paulo, Brazil.Show Abstract
This work reports on the utilization of silver and gold nanocubes as substrates for the surface-enhanced Raman scattering (SERS) detection of a wealth of pesticides. The nanocubes were obtained via the chemical reduction of Ag+ or AuCl4- ions in solution. Such nanostructures were then employed as substrates for the SERS detection of organochloride compounds, such as 2,6-dichloro-4-nitroaniline (Dicloran) and 2,4-dichloro-6-nitrophenol. In all cases, the Ag and Au nanocubes displayed high performances as SERS substrates and the characteristic Raman signals of the probed molecules displayed good signal to noise ratios at the micromolar range. In addition, density functional theory (DFT) calculations for normal Raman and SERS spectra were performed to obtain a reliable analysis of the specific moleculeâ€“surface interactions over the silver and gold substrates. Our results show that the prepared Ag and Au nanocubes can serve as versatile platforms for the development of new sensing techniques for the ultrasensitive analysis of various pesticides based on the SERS effect. Reference Costa, J. C. S.; Ando, R. A.; Santâ€™ana, A. C.; Rossi, L. M.; Santos, P. S.; Temperini, M. L. A.; Corio, P. Phys. Chem. Chem. Phys. 2009, 11, 7491â€“7498.
8:00 PM - KK11.6
Tunable Stop-gaps with Coupled Bright and Dark Plasmonic Lattice Resonances
R. K. Rodriguez1, Aimi
Gomez Rivas1 5.
Center for Nanophotonics, FOM Institute AMOLF c/o Philips Research, Eindhoven, Netherlands; 2,
Department of Electronic and Information Systems (ELIS), Ghent University, Ghent, Belgium; 3,
Optics Research Group, Delft University of Technology, Delft, Netherlands; 4,
Micro- and Nanophotonic Materials Group, University of Mons, Mons, Belgium; 5,
COBRA Research Institute, Eindhoven University of Technology, Eindhoven, Netherlands.Show Abstract
By tuning the radiative coupling of localized surface plasmons to diffracted orders, we demonstrate how tunable stop-gaps may be opened in the dispersion diagram of plasmonic crystals of nanorods. The stop-gap arises from the mutual coupling of Surface Lattice Resonances (SLRs), which are collective Fano resonances associated with counter-propagating surface polaritons. The different field symmetries of the high and low frequency coupled SLR bands lead to pronounced differences in light extinction over narrow spectral regions. We observe that standing waves of very narrow spectral width compared to localized surface plasmon resonances are formed at the high frequency band edge, while subradiant damping leads the low frequency band into darkness. We show how the dispersion of coupled bright and dark SLRs, the frequency width of the gap, and the in-plane momentum width of the standing waves, can all be tailored by tuning the form factor of the array, i.e., the dimensions of the nanorods which determine their polarizability. We elucidate the physics in terms of a coupled oscillator analog to the plasmonic crystal. Our model serves to estimate very high quality factors for SLRs, and relates the tunability of the stop-gaps to the coupling strength of the surface modes involved.
KK11.8 Transferred to KK9.5Show Abstract
8:00 PM - KK11.9
Plasmonic Engineering in Non-concentric Gold Nanoring Dimers
Materials & Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Dayton, Ohio, USA; 2,
School of Chemistry, Georgia Institute of Technology, Atlanta, Georgia, USA.Show Abstract
The advent in engineering plasmonic resonances in noble metal nanostructures led in recent years to a broad range of novel concepts, with applications in sensing, energy harvesting, or nonlinear optics, among others. In this work we probe non-concentric gold NRs (NC AuNRs) deposited on a Si3N4 substrate, which are based on geometries of concentric AuNR dimers we fabricated and characterized experimentally and theoretically. Finite difference time-domain simulations for NC AuNRs will be discussed in detail, regarding effects of structure size and substrate, as well as variation of the offset from the center of the AuNR, among other parameters that influence the optical response. Implications for application of this class of materials will be suggested.
8:00 PM - KK11.11
Separating Enhancement from Loss: Plasmonic Nanocavities in the Weak Coupling Regime
School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA.Show Abstract
By altering the electromagnetic density of states near an optical emitter, optical cavities can modify the emission properties of the emitter, either enhancing or suppressing emission depending on the degree of detuning between the emission frequency of the emitter and the resonance frequencies of the cavity. In the visible and near-IR part of the spectrum, such optical cavities are typically fabricated in dielectric material systems, where the low inherent loss of the materials and the ability to make highly reflective mirrors has enabled fabrication of cavities of very high quality. Recently, progress has been made in fabricating metal-based optical cavities containing coupled emitters. These cavities are capable of tightly confining light, leading to an electromagnetic density of states that is greatly modified spatially as opposed to spectrally. Here, we present measurements from a metal-based optical cavity containing coupled optical emitters that greatly modifies both the spectral and temporal characteristics of the coupled emitters. Our structure utilizes plasmonic hybridization between a silver nanowire and a planar silver substrate to tightly confine electromagnetic energy in the nano-scale gap between the nanowire and substrate. A layer of optical emitters within the gap (either organic dye molecules or colloidal nanocrystals) strongly interacts with the confined electric field, leading to a 1000-fold enhancement of the spontaneous emission rate of the coupled emitters. These results suggest that metal-based optical cavities can allow quantum cavity electrodynamics of intrinsically broad emitters such as colloidal quantum dots and organic dyes.
8:00 PM - KK11.12
Enhanced Full Band Photodetection through Collection of Plasmonic Hot Electrons
Materials Science and Engineering, Stanford Univ, Stanford, California, USA.Show Abstract
Surface plasmons on metallic surfaces have been widely studied due to their attractive optical properties. One of the key issues has been the inherent absorption loss in the metal, which often limits device performance. Here we show that this strong absorption can in fact be beneficial, by harvesting the high concentration of hot-electrons created within the metal. This principle is demonstrated in simple metal-insulator-metal (MIM) devices, where the hot electrons are extracted from the top metal by tunneling through the extremely thin insulator barrier, and collected in the lower electrode. Here we report plasmon-enhanced photodetection through hot carrier collection in grating structure MIM devices that donâ€™t suffer from the limited bandgap range in semiconductors. The key factor in realizing this is to properly design features on the metal surface to excite surface plasmons at any specific wavelength. The grating devices are optically excited under different polarizations to demonstrate surface plasmon excitation is responsible for the photocurrent, and current enhancement of more than 360% at 596 nm is observed. Linear dependence of the current on light power indicates a single-photon process during excitation of electrons.
8:00 PM - KK11.13
Comparing the Effects of Organophosphorus Induced Aggregation on Metallic vs. Bimetallic Plasmonic Nanoparticles
Chemistry, Western Michigan University, Kalamazoo, Michigan, USA.Show Abstract
Colorimetric sensors that selectively detect environmental pollutants in real time are becoming increasingly important areas of research. In particular, the design of materials that detect and discriminate between pollutants with similar molecular structures are in high demand. We have developed a series of colorimetric sensors based on silver (Ag), and gold (Au) metallic nanoparticles, and Ag/Au bimetallic nanoparticles. Particle size and shape were controlled through wet-chemical synthesis. The quality and the structure of the surface of the nanoparticles were found to play an important role in the detection process. The interaction of the nanoparticles with the pesticides ethion, malathion, parathion, fenthion and paraoxon was examined. We found that with proper control of particle size and composition, these nanoparticles are highly selective toward OP pesticides, giving specific changes in optical signal. The sensors can be tuned to have up to ppb detection limits. The presentation will demonstrate the rational choices in substituent selection for selective discrimination between organophosphorus compounds.
8:00 PM - KK11.15
Active Apertureless Near-field Imaging (AANI) of Optical Plasmonic Distribution
, Nanonics Imaging Ltd., Jerusalem, Israel; 2,
Selim & Rachel Benin School of Computer Science & Engineering, Hebrew University of Jerusalem, Jerusalem, Israel.Show Abstract
Scattering near-field scanning optical microscopy called ANSOM or sSNOM has been applied to look at plasmonic distribution. Unfortunately, the probes that need to be used in order to effectively scatter the plasmonic signal have significant perturbation on the plasmonic propagation because of the need to use probes with high dielectric constant to obtain effective signal to noise in such scattering experiments. In this paper, we will demonstrate the application of our development of multiprobe scan probe microscope technology for effective localized illumination of plasmonic structure with an apertured NSOM probe which produces all k-vectors. The propagating plasmons are imaged with an active fluorescent material embedded in a glass probe  with minimal perturbation of the plasmonic propagation. The results indicate that localized apertured NSOM illumination and active apertureless monitoring of plasmons has significant potential for investigating plasmonic structures. 1. A. Lewis and K. Lieberman, "Near-field Optical Imaging with a Non-evanescently Excited High-brightness Light Source of Sub-wavelength Dimensions," Nature 354, 214 (1991).
8:00 PM - KK11.16
Extraordinary Nonlinear Absorption in Three-dimensional Bow-tie Nanoantenna
Huntington2, Chul Hoon
Kim1 3, Wei
Wasielewski1 3, Teri
Odom1 2 3.
Chemistry, Northwestern University, Evanston, Illinois, USA; 2,
Material Science and Engineering, Northwestern University, Evanston, Illinois, USA; 3,
, Argonne-Northwestern Solar Energy Research (ANSER) Center, Evanston, Illinois, USA.Show Abstract
Extremely large nonlinear absorption was obtained from three-dimensional (3D), bowtie-shaped Au nanoantennas. Nonlinear light absorption can be substantially increased by localized electric fields excited around metal nanoparticles. We show that linear transmission spectra supported by FDTD calculations exhibit the strongest field enhancement at the LSP wavelengths. The imaginary part of the third-order nonlinear susceptibility (Im Ï‡(3)), characterized by open-aperture z-scan measurement, for the 3D bowties embedded in a dielectric material was measured to be 10-4 esu. The LSP-assisted nonlinear absorption of these 3D bowtie nanoantennas exceeded the reported values found in other metal nanoparticle-dielectric composites by more than two-orders of magnitude. These 3D nanoantennas can be used as a key element to increase the functionality for nanoscale nonlinear optical devices.
8:00 PM - KK11.17
Design, Fabrication and Characterization of Plasmonic Enhancers for Light-nanomaterial Interaction
Farrokh Baroughi1, Khadijeh
Electrical Engineering & Computer Science, South Dakota State University, Brookings, South Dakota, USA; 2,
Chemistry, University of South Dakota, Vermillion, South Dakota, USA; 3,
Nanoscience and Nanoengineering, South Dakota School of Mines and Technology, Rapid City, South Dakota, USA.Show Abstract
This article presents a systematic approach for design of 2.5 dimensional plasmonic crystals for enhanced light-nanomaterial interaction. A comprehensive study on plasmon resonance and the resulting near field enhancement in periodic arrays of gold and silver nanopillars as well as their dependence on geometry of nanopillars (diameter d, spacing s, and height h) as well as the excitation wavelength and angle was conducted utilizing 3D-finite difference time domain (FDTD) analysis. The study was utilized to design a plasmonic crystal (nanopillar arrays in square lattice with d, s, and h values of 310 nm, 620 nm, and 70 nm) with maximum plasmonic activity at 980 nm to couple with a thin layer of poly(methyl methacrylate) (PMMA) dispersed with upconversion nanocrystals of NaYF4: 3%Er, 17%Yb. The designed gold plasmonic crystal was fabricated by deposition of a 100 nm gold layer on a glass substrate followed by deposition of another 70 nm gold layer through electron beam patterned holes in PMMA and a following lift-off process. A PMMA layer dispersed with nanocrystals of NaYF4: 3% Er, 17%Yb with thickness of 105 nm was then deposited on the plasmonic crystal and spectroscopic measurements were conducted on the samples. A minimum in the measured reflection spectrum at 980 nm showed an excellent agreement between the design and measurement and confirmed the maximum plasmonic activity of the gold plasmonic crystal at 980 nm. The upconversion spectra of the upconversion nanopartciles in the PMMA matrix was obtained by a confocal microscope using 980 nm probe laser with 6 mW illumination intensity. The measurements revealed that the plasmonic crystal has led to an over 16X enhancement in the upconversion efficiency of the NaYF4: 3%Er, 17%Yb nanocrystals.
8:00 PM - KK11.18
Single DNA-tethered Nanodumbbells with a Narrow Distribution of Large Enhancement Factors in Surface-enhanced Raman Scattering
Lee2, Yung Doug
Chemistry, Soeul National University, Seoul, Republic of Korea; 2,
Laboratory for Advanced Molecular Probing (LAMP), NanoBio Fusion Research Center, Korea Research Institute of Chemical Technology, DaeJeon, Republic of Korea; 3,
School of Electrical Engineering and Computer Science & Inter-University Semiconductor Research Center (ISRC), Soeul National University, Seoul, Republic of Korea.Show Abstract
Constructing sophisticated plasmonic nanogap nanostructures with highly strong and quantitative surface-enhanced Raman scattering (SERS) signals and a narrow distribution of enhancement factors (EFs) is of significant importance in many research areas such as nanomaterials, plasmonics, Raman, chemical and biological sensing. Here, we extensively studied relationships between single-molecule SERS intensity, EF distribution over many particles, interparticle distance, particle size/composition and excitation laser wavelength using single-particle Raman measurement and 3D finite element method-based electromagnetic calculation with two different single-DNA-tethered Au-Ag core-shell nanodumbbell (GSND) dimer designs. Two GSND probes include â€œGSND-Iâ€ to study the effect of change in inter-particle gap distance from 4.8 nm to 0.2 nm or no gap and â€œGSND-IIâ€ to study the effect of change in Au core size with a fixed gap distance and shell thickness and change in excitation laser wavelength. We learned that synthesizing <1-nm gap (0.2 nm gap in this case) is a key to obtain high EF value (as high as 5.9x1013) with a narrow EF value distribution (between 1.9x1012 and 5.9x1013). In the case of GSND-II probes, a combination of >50-nm Au cores and 514.5-nm laser wavelength that matches well with Ag shell generated stronger SMSERS signals with a more narrow EF distribution than <50-nm Au cores with 514.5-nm laser or GSND-II with 632.8-nm laser.
8:00 PM - KK11.19
Evaluation of Plasmonic Nanoparticles Behavior as They Transitions from Natural to Engineered Systems by Monitoring Ligand Exchange Kinetics Using Fluorescence Resonance Energy Transfer
D'Unger1 2, Thompson
Mefford1 2, Christopher
Material Science & Engineering, Clemson University, Clemson, South Carolina, USA; 2,
Center for Optical Materials Science and Engineering Technologies, Clemson University, Clemson, South Carolina, USA; 3,
Chemical & Biomolecular Engineering, Clemson University, Clemson, South Carolina, USA.Show Abstract
Significant research in nanotechnology has occurred recently in all areas of science, including biomedical, electronics, and consumer products. However, little is still known about the fate of nanoparticles as they transition from engineered to environmental systems. With an increasing rate of nanomaterials being used, concern has risen about their potential human or environmental harm. An important factor to consider in these systems is surface functionality, as this is one of the main contributors to particle stability and end use. In light of this, an investigation was conducted on gold particles to compare the response of different ligands on the surface of nanoparticles. The goal of this study is to measure the hierarchy of binding constituents, rate of ligand attachment and displacement, and a soil retention study in order to understand the interactions of different surface ligands and the kinetics of ligand exchange on plasmonic nanoparticles. These values are determined by measuring the exchange of non-fluorescent with fluorescent ligands on the surface of plasmonic nanoparticles. In this study gold nanoparticles are used as they have well-defined â€œquenchingâ€ of the photoluminescence of dye molecules at the surface. We utilize this â€œquenchingâ€ as tool to measure the rate of ligand exchange on the surface by observing the change in fluorescence of bound fluorophors using FRET. In order to understand how naturally occurring ligands will interact in both aquatic and soil systems, a wide array of fluorescently labeled common stabilizing ligands was synthesized via NHS chemistry. The displacement of these ligands from the surface of the gold particles could then be tracked by an increase in their photoluminescent signal. Calibration curves were created for each ligand so that the concentration of displaced ligands could be determined during reactions. The exchange of ligands were measured using three techniques; introducing fluorescently tagged ligands to a system of Au nanoparticles, introducing free non-fluorescent ligands to a system of Au nanoparticles with bound fluorescently tagged ligands, and using a combination of the first two with two different fluorescent molecules. In the first scenario the exchange can be measured by observing a decrease in fluorescent intensity upon binding. The second allows fluorescent intensity to increase as surface ligands are replaced by free ligands. Finally, in the third scenario the fluorescent intensities of the different molecules changes depending on which ligands bind to the surface of the nanoparticles. This investigation has provided a hierarchy of ligands and their exchange kinetics. The knowledge gained in this study will help in predicting the behavior nanoparticles will exhibit when they enter natural systems. Knowing how nanoparticles will behave in these systems may provide further insight into any harmful effects on both humans and the environment, as well as how to manage these particles.
8:00 PM - KK11.20
Self-assembled Nanocrystals for Generating Plasmonic Hot Spots
, UC San Diego, La Jolla, California, USA.Show Abstract
Ideal plasmonic nanojunctions occur when high-curvature metal surfaces are separated by small nanometer-sized gaps, producing intense â€œhot spotsâ€ due to electromagnetic field localization within the gaps. While direct-write techniques such as electron-beam lithography are able to generate complex nanostructures with impressive spatial control, these methods encounter difficulties in fabricating gaps on the order of a few nanometers and in the scalable manufacturing of nanojunction arrays. Here, we fabricate nanojunctions by organizing polymer-grafted nanoparticles directly within a supported polymer thin-film matrix. We engineer the non-specific nanoparticle interactions that modulate the relative strengths of attractive van der Waals and repulsive steric forces by addressing simple parameters such as polymer chain length, rigidity, and grafting density. We demonstrate this by fabricating a nanoparticle thin-film that switches from one nanoparticle orientation (edge-connected) to another (face-connected), producing a stimulus-responsive change in the plasmonic response that is consistent with electric field calculations.
8:00 PM - KK11.21
Collective Plasmon Mode Excited on Multi-dimensionally Assembled Metallic Nanoparticles
Institute for Materials Chemistry and Engineering, Kyushu University, Fukuoka, Japan.Show Abstract
We report a new concept to tune localized surface plasmon resonance (LSPR) band of two dimensional (2D) crystalline metallic nanoparticle (NP) sheets in combination with layer-by-layer structures on metal substrates and nano-domain formations in mixed monolayers. In principle, the multilayerd 2D AgNP crystalline sheets fabricated by the Langmuir-Schaefer method keep the LSPR band position at the same wavelength (Î»max ~ 465 nm) on quartz , however, they change their colors (wavelength and intensity) drastically on Au or Ag substrates depending on the number of layers (1-5 layers). The response of the LSPR bands was absolutely non-linear, which exhibits the maximum absorption at the layer number of 2 or 3, while the LSPR band position shifted linearly to the longer wavelength. We investigated the mechanism of interlayer coupling by use of AuNPs sheet (Î»max ~ 630 nm) as a marker. The data revealed the complexity of electromagnetic interaction within the layered films; i.e., depending on the layer position of the integrated AuNPs monolayer, the color of the multilayered films changed largely, even though the total layer numbers are the same (e.g. AgNPs sheet : AuNPs sheet = 4:1). Another way to tune the LSPR band is nano-phase segregation in mixed films. When AgNPs and AuNPs were spread at air-water interface from the mixed solution, the AuNPs always formed island-like domains in the AgNPs matrix phase. The color of the mixed film varied in a wide range due to the size of domains determined by the AgNPs/AuNPs mixing ratio. These phenomena were reasonably interpreted by FDTD calculation in consideration of domain size effect and interparticle coupling between AgNP and AuNP.  Toma M, Tamada K, et al, Phys. Chem. Chem. Phys. 13, 7459 (2011).
8:00 PM - KK11.22
Wrinkle Assisted Linear Assembly of Plasmonic-core/Soft-shell Particles: A Versatile Approach towards Anisotropic Nanostructures
Physical Chemistry I, University of Bayreuth, Bayreuth, Bavaria, Germany; 2,
Physical Chemistry II, University of Bayreuth, Bayreuth, Bavaria, Germany; 3,
Theoretical Chemistry II, University of Bayreuth, Bayreuth, Bavaria, Germany; 4,
Physical Chemistry III, University of Bielefeld, Bielefeld, NRW, Germany.Show Abstract
We demonstrate the controlled linear assembly of silver-poly-N-isopropylacrylamide (Ag-PNIPAM) hybrid core-shell particles via a wrinkle assisted deposition method . The particles were deposited on glass substrates by a spin-release process from poly-dimethylsiloxane (PDMS) templates with different wavelengths yielding linear assembled particle arrays. The assemblies show a high degree of order on cm scale, which is already visible by the naked eye due to strong iridescent colors caused by interference of the incident light with the periodic particle arrays. The ordering is also confirmed by laser diffraction experiments, where diffraction is observed up to the fourth order. Structural investigations employing SEM reveal anisotropy of the assemblies on two length scales, macroscopically guided through the wrinkle structure and locally due to deformation of the soft polymer shell leading to smaller inter-core separations as compared to assembly on flat substrates without confinement. Additionally, radial distribution functions (RDF) are shown, clearly highlighting the impact of confinement on nearest neighbor distances and symmetry. These results are compared to results obtained from wrinkle assisted assembly of hard spheres. Monte-Carlo simulations confirm that the observed symmetries for hard-core/soft-shell particles are attributed to the soft interaction potential. In addition, results from polarization dependent UV-vis spectroscopy indicate Plasmon coupling of the silver cores. The presented method is a fast, cost effective technique to prepare anisotropic structures on large areas.  M. MÃ¼ller, M. Karg, A. Fortini, T. Hellweg, A. Fery, in preparation  N. Pazos-PÃ©rez, W. Ni, A. Schweikart, R. A. Alvarez-Puebla, A. Fery, L. M. Liz-MarzÃ¡n, Chemical Science, 2010, 1, 174-178.
KK11.23 Transferred to KK12.3Show Abstract
8:00 PM - KK11.26
Unidirectional Broadband Radiation of Honeycomb Plasmonic Antenna Array
, Sabanci University, Istanbul, Turkey.Show Abstract
Emerging plasmonic and photovoltaic applications benefit from effective interaction between optical antennas and unidirectional incident light over a wide spectrum. In this study, we propose a honeycomb array of plasmonic nanoantennas with broken symmetry for obtaining a unidirectional radiation pattern over a wide spectrum. The honeycomb nanoantenna array is based on a hexagonal grid with periodically arranged nanostructure building blocks. To analyze the far-field optical distribution and spectral behavior of the plasmonic antenna honeycomb, a two-dimensional Wigner-Seitz unit cell is used to represent the nanostructure building block of broken symmetry. When combined with periodic boundary conditions, superposition of the fields from a single asymmetric building block generate far-zone optical fields lead to constructive or destructive interference in different directions. The constructive interference along the array's normal direction engenders unidirectional radiation. Consequently, due to the broken symmetry of the Wigner-Seitz cell, multiple resonances are supported by the plasmonic antenna honeycomb array over a broad spectrum.
8:00 PM - KK11.27
Plasmon Propagation along a Chain of Metallic Nanoparticles: Effects of a Magnetic Field and a Liquid Crystalline Environment
Physics, Ohio State University, Columbus, Ohio, USA.Show Abstract
It is well established that plasmonic waves can propagate along chains of closely spaced metallic nanoparticles. Their dispersion relations are readily calculated within the quasistatic approximation, using the tight-binding method, and even including higher multipole moments. In this work, we present a calculation of these dispersion relations in the presence of either an external magnetic field, or an anisotropic environment such as a nematic liquid crystal. With an external magnetic field applied parallel to the chain, we show that a linearly polarized plasmonic wave is Faraday-rotated as it propagates along the chain, and we calculate both the rotation angle and the depolarization of this wave per unit chain length, within the quasistatic approximation, including single-particle damping. If the chain is immersed in a nematic liquid crystal with principal axis parallel to the chain, we show that both the width and the center of the plasmonic band are modified. We calculate the modified dispersion relations using the tight-binding method, again including single-particle damping. Both calculations are carried out using a generalized depolarization tensor formalism to compute the dipole field of a single metallic grain in the presence of these external perturbations. These results may be useful in developing nanoscale optical devices. For example, because the dielectric tensor of a nematic liquid crystal depends on both temperature and applied electric field, the dispersion relations of plasmonic waves propagating along a chain of metal particles may be controllable by temperature and electric field.  M. L. Brongersma, J. W. Hartman, and H. A. Atwater, Phys. Rev. B62, R16356 (2000).  S. Y. Park and D. Stroud, Phys. Rev. B69, 125418 (2004).  S. Y. Park and D. Stroud, Appl. Phys. Lett. 85, 2920 (2004).
8:00 PM - KK11.28
Critical Coupling in Plasmonic Resonator Arrays
Physics, Bilkent University, Ankara, Turkey.Show Abstract
We present critical coupling of electromagnetic waves to plasmonic cavity arrays fabricated on MoirÃ© surfaces. The critical coupling condition depends on the superperiod of MoirÃ© surface, which also defines the coupling between the cavities. Complete transfer of the incident power can be achieved for traveling wave plasmonic resonators, which have relatively short superperiod. When the superperiod of the resonators increases, the coupled resonators become isolated standing wave resonators in which complete transfer of the incident power is not possible. Dark field plasmon microscopy imaging and polarization dependent spectroscopic reflection measurements reveal the critical coupling conditions of the cavities. We image the light scattered from SPPs in the plasmonic cavities excited by a tunable light source. Tuning the excitation wavelength, we measure the localization and dispersion of the plasmonic cavity mode. Dark field imaging has been achieved in the Kretschmann configuration using a supercontinuum white light laser equipped with an acoustooptic tunable filter. Polarization dependent spectroscopic reflection and dark field imaging measurements are correlated and found to be in agreement with FDTD simulations.
8:00 PM - KK11.29
Surface Assembly of Nanorod Dimers and Arrays: Fine Control over Plasmonic Properties through Programmed Coupling
Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA; 2,
Chemistry, Georgia Institute of Technology, Atlanta, Georgia, USA; 3,
Materials and Manufacturing Directorate, Air Force Research Laboratories, WPAFB, Ohio, USA.Show Abstract
Coupling effects in plasmonic nanostructures are of tremendous interest due to the potential to actively modulate the plasmon resonances relative to individual nanoparticles and the strong field enhancements that are observed in small gaps between adjacent nanoparticles. In this report, we demonstrate the synthesis and surface assembly of nanorod dimers and arrays. Gold nanorod dimers and arrays, with rod diameter and length of 50 and 100 nm respectively, were synthesized in porous anodic alumina templates through electrodeposition allowing for fine control (<2 nm) of the nanorod length and the size of the gap between rods. High-resolution dark field hyperspectral imaging was used to image and measure polarized UV-Vis scattering spectra from individual dimer pairs fabricated with varying gap size (ranging from 2 to 20 nm). The polarized UV-Vis spectra were able to clearly resolve the transverse and longitudinal plasmon peaks and demonstrated large red shift in longitudinal peak position (nearly 200 nm) as the dimer gap was reduced from 20 to 2 nm. The shift in the longitudinal peak with decreasing gap size correlated well with the expected results based on discrete dipole approximation simulations. These results demonstrate the ability to fabricate and homogeneously assemble over large areas nanorod dimers and arrays with programmable control over plasmonic properties through fine control over rod length and gap size. Moreover, this approach is a low-cost complement to traditional top-down approaches that can easily be extended to asymmetric multi-metal plasmonic systems. Finally, the results demonstrate the ability to precisely image and characterize the plasmonic properties from an individual dimer pair using high-resolution hyperspectral imaging.
8:00 PM - KK11.30
Near-Infra-Red (NIR) Metatronic Filter Elements as Building Blocks for the NIR Filter Metamaterials
Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, USA.Show Abstract
We design, fabricate, and test metamaterial building blocks functioning as optical nanocircuits in the NIR regime. We explore arrays of nanorods with rectangular cross sections, made of Transparent Conductive Oxides (TCOs), such as indium tin oxides (ITO). Using the equivalent circuit theory and FDTD (Finite-difference time-domain) simulations, we design and analyze the nanoscale circuit element functionalities of such building blocks. We show that we can control the functionality of these metatronic circuits by tailoring the cross sectional dimensions and the pitch of the TCO nanorods arrays. Furthermore, such nanocircuits can also function differently for different polarization of the incident E-field, thus making such circuits â€œstereo-circuitsâ€. When nanorods are illuminated by E-field vector parallel to the rods, the array should function as the â€œparallelâ€ combination of elements, and the parallel L-C circuit may act as a bandpass filter. However, when the E-field vector is polarized perpendicular to the rods the array may behave as â€œseriesâ€ combination and it indeed acts as a bandstop filter. We have fabricated and tested several samples of such nanorods made of ITO, and have shown the agreement of the measurement results for the spectral response of the fabricated ITO nanorods arrays with the calculations and simulations. In this presentation, we will present our theoretical and experimental results for NIR filter metamaterials using the TCO nanorod arrays functioning as the optical nanocircuits.
KK11.32 Transferred to KK5.3Show Abstract
8:00 PM - KK11.33
Hybrid Metal/Semiconductor Nanostructures: Cloaking and More
Materials Science and Engineering, Stanford University, Stanford, California, USA; 2,
Electrical and Systems Enigineering, University of Pennsylvania, Philadelphia, Pennsylvania, USA.Show Abstract
It is well known that metallic nanostructures have the ability to concentrate light into deep subwavelength volume due to surface plasmon resonance. Semiconductor nanostructures, such as Si/Ge nanowires could also have strong interaction with light due to excitation of dielectric resonances. In our work, it is shown that by carefully combining metal and semiconductor materials within subwavelength volume, such hybrid nanostructures could have novel light-matter interactions due to drastically different materials properties of metals and semiconductors. We have demonstrated a gold coated silicon nanowire could act as an "invisible" photodetector due to the process known as "plasmonic cloaking". We could further show such hybrid metal/semiconductor with interesting scattering and absorption properties that differ from both metal and semiconductor nanostructures alone due to the coupling of resonances excited in each component. These results could shine light on the design of next generation of optoelectronic devices with complex functionalities.
8:00 PM - KK11.34
Spectroscopic Imaging of Metal-enhanced Upconversion on Plasmonic Substrates
Baroughi3, P. Stanley
Nanoscience and Engineering, South Dakota School of Mines and Technology, Rapid City, South Dakota, USA; 2,
Chemistry Department, University of South Dakota, Vernillion, South Dakota, USA; 3,
Electrical and Computer Engineering, South Dakota Statue University, Brookings, South Dakota, USA.Show Abstract
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, including: Ag nano-wires synthesized by wet chemistry methods, and lattices of Au nano-pillars fabricated by electron beam lithography, the latter of which are designed to support a surface plasmon polariton at frequencies which are near-resonant with the rare-earth ion (Yb3+) absorption. 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 field distributions near the metallic nanostructures and their frequency-dependent reflectivity.
8:00 PM - KK11.35
A Study on the Graded-index Photonic Crystals as Efficient Input and Output Couplers for Photonic Crystal Waveguides
Electrical Electronics Engineering, Bilkent University, Ankara, Turkey.Show Abstract
We consider a graded-index (GRIN) photonic crystal (PC) as an input and output coupler for a photonic crystal waveguide (PCW) and investigate the enhanced coupling efficiency figures. We show that the designed GRIN PC supports modified versions of the Hermite-Gaussian modes. An analogy in between the examined GRIN PC and the quadratic GRIN medium is shown to be useful in understanding the propagation of the electromagnetic waves inside the GRIN PC. We numerically and experimentally demonstrate that by employing the GRIN PC it is feasible to focus spatially wide input pulses into the narrow entrance of the PCW, hence improving the input coupling efficiency as high as 8.27 dB with an insertion loss -1.62 dB. At the same time, the highly diverging beam exiting from the PCW end with circular wave fronts are transformed into planar wave fronts. As a result, the divergence angle of the beam is substantially reduced from 70 degrees to 11 degrees. Accordingly, the confinement of the out-coupled beam resulted in a 90% reduction in the half-power beam width (HPBW) values. A directional beaming efficiency up to 76% is reported in the accompanying microwave experiments. HPBW values down to 7 degrees are measured.
8:00 PM - KK11.36
Unidirectional Transmission in Photonic-crystal Gratings
Electrical Electronics Engineering, Bilkent University, Ankara, Turkey.Show Abstract
In the limiting case of the directional selectivity such a device that would allow (nearly) total transmission in one direction and no transmission in the opposite direction within the same propagation channel could be considered as the electromagnetic counterpart of a diode. The conventional approach to achieve the unidirectional transmission in passive devices is based on the use of the anisotropic or nonlinear materials. In particular, the strongly pronounced unidirectional transmission has been demonstrated for the one-dimensional photonic crystals (PCs) and for the stacks of the two-dimensional PCs, in which anisotropic materials were utilized. Directional waveguides have been realized in PCs with broken time-reversal symmetry. In this paper, we investigate the directional selectivity in the PC gratings in the microwave regime at beam-type illumination. The simulations and the microwave experiments are performed for a wide frequency range that involves the first five PC bands (Floquet-Bloch waves), which are distinguished in terms of their respective dispersion features. The presented results include the transmission spectra of the examined structures for the plane-wave illumination, the frequency response of the transmittance for Gaussian-beam and horn antenna illuminations, and the angular distributions of the transmittance, at a proper value of the angle of incidence. We have demonstrated unidirectional transmission in the PC gratings with one-side echelette-type corrugations at beam-type illumination. Simulation results obtained for the plane-wave and Gaussian-beam illuminations, and the experimental results for the microwave horn antenna illumination were presented and analyzed. We have observed a good connection between the features detected at plane-wave, Gaussian-beam and horn antenna illuminations.
8:00 PM - KK11.37
Photo-luminescence Enhancement Using Plasmon Resonant Cavities
Engineering Technologies Division, Lawrence Livermore Nat'l Lab, Livermore, California, USA.Show Abstract
We developed plasmonic resonant cavities based on vertical metallic nanowire arrays for enhancing the efficiency of photoluminescent dyes. Gap plasmon modes are excited in the space between two adjacent nanowires when the roundtrip phase change is a multiple of 2Ï€. We demonstrate continuous tuning of plasmon resonances in the visible (400 to 800 nm) by adjusting the geometrical dimensions of the nanowires (radius, height) as well as the refractive index of the materials immersing the nanowire array. An increase in dye absorbance is observed when the plasmon resonance is aligned with extinction maximum of the dye. The material luminescence is also enhanced when the plasmon resonance is aligned with the emission wavelength. We further discuss the possibility to fabricate of a two resonance plasmon laser that employs surface plasmons to enhance both absorbance and emission for a more efficient pumping of the gain medium.
8:00 PM - KK11.40
Enthalpy-driven Preconcentration of Molecules on Fluid-fluid Interface
Jeong1, Won Bo
Chemical and Biomolecular Engineering, Sogang University, Seoul, Republic of Korea.Show Abstract
Preconcentration of a molecule can be considered as an essential step when the concentration of target is very low. Typically, preconcentration is time-, cost- and labor- consuming. Here we report simple yet innovative preconcentration method based on enthalpy-driven accumulation of molecules at fluid-fluid interface. Numerical calculation reveals that local concentration of molecules at water/oil interface can be up to 100 times higher than that in water by controlling the difference in the diffusivities of the molecules in two fluids. We test the feasibility of our method by applying to surface-enhanced Raman scattering (SERS). Even though as-made colloidal gold nanorod without any further treatment is directly used as a SERS-active probe, 1 nM of rhodamine 6G is readily detectable based on our preconcentration scheme. We believe that this preconcentration method can be easily applied to a molecular detection in ranges from molecular diagnostics to environmental monitoring.