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
, University of Stuttgart, Stuttgart, Germany.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 . 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 . References:  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).  C. Matthiessen, A. N. Vamivakas, and M. Atatüre, “Subnatural linewidth single photons from a quantum dot”, Phys. Rev. Lett. 108, 093602 (2012).  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).  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
Physics Dept and Nano and Micro Device Center, University of Alabama in Huntsville, Huntsville, Alabama, USA.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
, University of Salford, Manchester, United Kingdom; 2,
, University of Manchester, Manchester, United Kingdom; 3,
, Institute of Physics, Belgrade, United Kingdom; 4,
, University of Lancaster, Lancaster, United Kingdom.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 . 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 , whilst taking into account the important second-order effect of piezoelectricity in this III-N material system . 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 . 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.  R. M. Stevenson, R. J. Young, P. Atkinson, K. Cooper, D. A. Ritchie, and A. J. Shields, Nature (London) 439, 179 (2006)  S. Tomic and N. Vukmirovic, Phys. Rev. B 79, 245330 (2009)  J. Pal, G. Tse, V. Haxha, M. A. Migliorato, and S. Tomic, Phys. Rev. B 84, 085211 (2011) 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
Physics of Complex Systems, Weizmann Institute of Science, Rehovot, Israel; 2,
Electron Microscopy Unit, Weizmann Institute of Science, Rehovot, Israel.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 . 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 . 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.  B. Lounis, M. Orrit, Rep. Prog. Phys. 68, 1129 (2005).  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
Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.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 -
3:30 PM - *CC8.06
Spins and Photons of Quantum Dots
Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom.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
, Naval Research Lab, Washington, District of Columbia, USA.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
Bi1 3, Taichi
, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA; 2,
Department of Materials Science and Engineering, University of Delaware, Delaware, Delaware, USA; 3,
, Micron Technology, Boise, Idaho, USA.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
Department of Physics, University of Cagliari, Monserrato, Sardinia - Cagliari, Italy; 2,
Centro Grandi Strumenti d'Ateneo, Università di Cagliari, Monserrato, Sardinia - Cagliari, Italy; 3,
Department of Chemistry, The University of Chicago, Chicago, Illinois, USA.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
Materials Science and Engineering, University of Arizona, Tucson, Arizona, USA; 2,
Electrical and Computer Engineering, University of Arizona, Tucson, Arizona, USA; 3,
Optics Research Lab, Canon, U.S.A. Inc, Tucson, Arizona, USA.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
Joo2, Dong June
Department of Chemical & Biological Engineering, Korea University, Seoul, Republic of Korea; 2,
Department of Physics, Korea University, Seoul, Republic of Korea.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
School of Science and Technology, Nottingham Trent University, Nottingham, NG11 8NS, United Kingdom; 2,
Dept of Materials Science and Engineering, University of Ioannina, Ioannina, GR-45110, Greece; 3,
Dept of Physics, University of Ioannina, Ioannina, GR-45110, Greece.Show Abstract
We have recently reported the photosensitivity of Aluminium Nitride (AlN) films with embedded silver nanospheres . 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.  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
Nishio1 2, Hideki
, KAST, Sagamihara, Kanagawa, Japan; 2,
, Tokyo Metropolitan Univ., Hachioji, Tokyo, Japan.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.  T. Kondo, F. Matsumoto, K. Nishio, H. Masuda, Chem. Lett., 37, 466 (2008).  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
Department of Materials Science & Engineering, North Carolina State University, Raleigh, North Carolina, USA.Show Abstract
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
Pena Rodriguez1, Antonio
Instituto de Fusión Nuclear, Universidad Politécnica de Madrid, Madrid, Madrid, Spain; 2,
Institut de Ciència de Materials de Barcelona, Consejo Superior de Investigaciones Científicas, Bellaterra, Barcelona, Spain; 3,
Instituto de Física, Universidad Autónoma de Puebla, Puebla, Puebla, Mexico.Show Abstract
Fano resonances (FRs) are typical spectral features caused by the coupling of a discrete state with a continuum . This phenomenon has been known for many years in atomic physics and constitutes the basis for the electromagnetically induced transparency (EIT) ; however, only recently it has been achieved in all-plasmonic systems . In addition to fundamental scientific interests, plasmonic Fano resonances in strongly coupled systems give rise to the so-called plasmon-induced transparency (PIT) , 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 . 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
Physics, Queens College, Queens, New York, USA.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) . 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, 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
Fujita2 4, Mingwei
Eda3 5, Manish
Materials Science and Engineering, Rutgers University, Piscataway, New Jersey, USA; 2,
WPI Advanced Institute for Materials Research, Tohoku University, Sendai, Japan; 3,
Physics, National University of Singapore, Singapore, Singapore; 4,
, JST, PRESTO, Saitama, Japan; 5,
Chemistry, National University of Singapore, Singapore, Singapore.Show Abstract
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 . 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.  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
Walsh1 2, Luca
Electrical and Computer Engineering, Boston University, Boston, Massachusetts, USA; 2,
Nanomaterials Science Team, US Army NSRDEC, Natick, Massachusetts, USA.Show Abstract
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
Electrical and Computer Engineering, National University of Singapore, Singapore, Singapore; 2,
, Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*Star), Singapore, Singapore.Show Abstract
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
Zettsu1 3, Nagahiro
Saito1 2 3.
Materials, Physics, and Energy Engineering, Nagoya University, Nagoya, Japan; 2,
EcoTopia Science Institute, Nagoya University, Nagoya, Japan; 3,
Green Mobility Corraborative Center, Nagoya University, Nagoya, Japan.Show Abstract
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
College of Optics and Photonics, University of Central Florida, Orlando, Florida, USA; 2,
Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA; 3,
Department of Mathematics, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA; 4,
Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.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
Institute of Solid State Physics, Friedrich Schiller University Jena, Jena, Germany.Show Abstract
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
Department of Physics, Boston College, Chestnut Hill, Massachusetts, USA.Show Abstract
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
Department of Physics, University of Alabama in Huntsville, Huntsville, Alabama, USA; 2,
Nano and Micro Device Center, University of Alabama in Huntsville, Huntsville, Alabama, USA.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
Park1 2, Palak
, ETH Zurich, Zurich, Switzerland; 2,
, University of Minnesota, Minneapolis, Minnesota, USA.Show Abstract
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
Engel1, S. R. c.
Chemistry, Northwestern University, Evanston, Illinois, USA; 2,
Material Science, Northwestern University, Evanston, Illinois, USA.Show Abstract
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
Physics, KAIST, Yousung-Gu, Daejeon, Republic of Korea.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
Advanced Materials Engineering, Kookmin Univ., Seoul, Republic of Korea.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
Niidome1 2, Naotoshi
Nakashima1 2 3.
, Kyushu University, Fukuoka, Japan; 2,
, I2CNER, WPI, Fukuoka, Japan; 3,
, CREST, JST, Tokyo, Japan.Show Abstract
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
Physics, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Republic of Korea; 2,
Physics, Korea University, Seoul, Republic of Korea.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
Physics, The Chinese University of Hong Kong, Hong Kong, Hong Kong.Show Abstract
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
, The Chinese University of Hong Kong, Hong Kong, China.Show Abstract
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
Chemistry, Middle East Technical University, Ankara, Turkey; 2,
Chemical Engineering and Applied Chemistry, Atilim University, Ankara, Turkey.Show Abstract
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
College of Engineering, Temple University, Philadelphia, Pennsylvania, USA.Show Abstract
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
College of Engineering, Temple University, Philadelphia, Pennsylvania, USA; 2,
Brockhouse Institute for Materials Research, McMaster University, Hamilton, Ontario, Canada.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
, Washington University in St. Louis, St. Louis, Missouri, USA.Show Abstract
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
Hong1 2, Jihye
Huh2 4 5, Seungjoo
Haam2 3, Dae Sung
Department of Biomedical Engineering, Yonsei University, Wonju, Republic of Korea; 2,
YUHS KRIBB Medical Convergence Research Institute, Yonsei University, Seoul, Republic of Korea; 3,
Department of Biomedical Engineering, Yonsei University, Seoul, Republic of Korea; 4,
Department of Radiology, College of Medicine, Yonsei University, Seoul, Republic of Korea; 5,
Severance Biomedical Science Institute (SBSI), Yonsei University, Seoul, Republic of Korea.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
Materials Science and Engineering, EPFL, Lausanne, Switzerland; 2,
Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, USA; 3,
Division of Physical Sciences and Engineering, Solar and Photo-voltaics Engineering Center, KAUST, Thuwal, Saudi Arabia.Show Abstract
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
Grad. School of Science, Hiroshima Univ., Higashi-Hiroshima Hiroshima, Japan; 2,
N-BARD, Hiroshima Univ., Higashi-Hiroshima Hiroshima, Japan.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, 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
, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea.Show Abstract
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
Physics, University of Memphis, Memphis, Tennessee, USA.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) and ZnO (0.019/min)  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:  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).  K. Tanaka, K. Padermpole, T. Hisanaga, Water Res., 34, 327 (2000).  S.X. Liu, Z. P. Qu, X. W. Han, C. L. Sun, Catalysis Today, 93, 877 (2004).  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
Laser Processing Group, Instituto de Optica, CSIC, Madrid, Madrid, Spain; 2,
Institut PPRIME, UPR 3346, CNRS, Université de Poitiers, Chasseneuil, France.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 . 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.  U. Kreibig and M. Vollmer, Optical properties of metal clusters, Springer (1995)  N.J. Halas et al., Chem. Rev. 111 (2011) 3913  E. Hao et al. J. Chem. Phys. 120 (2004) 357  H. Kuwata et al. Appl. Phys. Lett. 83 (2003) 4625  I. Zoric et al., ACS Nano 5 (2011) 2535  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
Niidome1 2, Naotoshi
Nakashima1 2 3.
, Kyushu University, Fukuoka, Japan; 2,
, I2CNER, WPI, Fukuoka, Japan; 3,
, CREST, JST, Tokyo, Japan.Show Abstract
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
, Temple University, Philadelphia, Pennsylvania, USA.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
Maria Beatriz1, Bornacelli
, Instituto de Fisica. Universidad Nacional Autonoma de Mexico, Mexico, DF, Mexico; 2,
, Centro de Investigacion en Energia. Universidad Nacional Autonoma de Mexico, Temixco, Morelos, Mexico; 3,
, Centro de Ciencias Aplicadas y Desarrollo Tecnologico. Universidad Nacional Autonoma de Mexico, Mexico, DF, Mexico.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
Adu1 5, Pralav
Physics, The Pennsylvania State University, Altoona College, Altoona, Pennsylvania, USA; 2,
Physics, The Pennsylvania State University, University Park, Pennsylvania, USA; 3,
Energy and Mineral Engineering, The Pennsylvania State University, University Park, Pennsylvania, USA; 4,
Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, Pennsylvania, USA; 5,
Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania, USA; 6,
Bioengineering, The Pennsylvania State University, University Park, Pennsylvania, USA; 7,
Chemistry, The Pennsylvania State University, Altoona College, University Park, Pennsylvania, USA.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
, Japan Advanced Institute of Science and Technology, Nomi City, Japan.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
Institute of Optics and Atomic Physics, TU Berlin, Berlin, Germany.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. , 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 . 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  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.  H. J. Simon and J. G. Watson, Optical Second-Harmonic Generation with Surface Plasmons in Silver Films, Phys. Rev. Lett. 33, 1531 (1974)  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
, California Institute of Technology, Pasadena, California, USA.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 , 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  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
Department of Chemistry, Kwansei Gakuin University, Sanda, Japan; 2,
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Japan; 3,
Department of Macromolecular Science and Engineering, Kyoto Institute of Technology, Kyoto, Japan.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
Lewis1 2, Rimma
Applied Physics, Hebrew University of Jerusalem, Jerusalem, Israel; 2,
Selim & Rachel Benin School of Computer Science & Engineering, Hebrew University of Jerusalem, Jerusalem, Israel; 3,
, Nanonics Imaging Ltd., Jerusalem, Israel.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.