Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session X28: Focus Session: Optical Properties of Nanostructures VII: Surface Plasmons and Periodic Arrays |
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Sponsoring Units: DMP Chair: Ho-Bun Chan, University of Florida Room: Morial Convention Center 220 |
Friday, March 14, 2008 8:00AM - 8:12AM |
X28.00001: Plasmonic propagation along Metal/Semiconductor/Metal nanowires Laetitia Bernard, Marleen H. van der Veen, Daniel Turner-Evans, Eric R. Dufresne, Mark A. Reed, Kwan Skinner, Sean Washburn Recent advances demonstrated metallic nanowires as structures allowing selective coupling of photons to fluctuations in the surface density of electrons, and the propagation of these plasmon modes along the wire. We report here the observation of such propagating plasmons in heterogeneous metal/semiconductor/metal nanowires. Specifically, we excite one end of a Au/CdSe/Au nanowire with focused laser light and demonstrate the coupling of photons into the plasmon modes of the wire. These modes propagate along the wire, being emitted as elastically scattered photons, exclusively at the metal/semiconductor interfaces and the distal end. Through control of the excitation wavelength and wire composition, we gain insights about the nature of the plasmon propagation through CdSe, allowing direct comparison with standard metal studies. This contributes to the growing interest in plasmonics within nanoscale devices by extending it to semiconductor materials, and goes towards the integration of optics with nanotechnology. [Preview Abstract] |
Friday, March 14, 2008 8:12AM - 8:24AM |
X28.00002: Plasmonic Interfaces for Electro-Optic Characterization of Molecular Junctions Marleen H. van der veen, Laetitia Bernard, Jason Merrill, Eric R. Dufresne, Mark A. Reed Metallic nanowires have interesting optical applications that make them promising platforms for sensing applications. The optical properties originate from the excitation of surface plasmon polaritons with light. We use this phenomenon to develop new spectroscopic tools to characterize the nature and details of the molecular structures within active regions of nanometer-scale devices. To achieve optical excitation at the nanometer-scale, we use a far field plasmon launching and emission technique based on nanowires coupled to molecular junctions. It is shown that plasmons can couple efficiently across small interfaces and can propagate along crossed nanowires. Furthermore, the light emitted as elastic scattered photons can be used to selectively couple light into the region of molecules for optical excitation. The possibility of doing local optical excitation of molecules simultaneously with their current-voltage measurements could lead to a new sensing platform for molecules based on plasmonic interfaces. [Preview Abstract] |
Friday, March 14, 2008 8:24AM - 8:36AM |
X28.00003: Controllable evanescent field coupling between metallic bilayers of subwavelength apertures Z. Marcet, J. Paster, H. B. Chan, D. W. Carr, J. E. Bower, R. Cirelli, F. P. Klemens, W. M. Mansfield, J. F. Miner, C. S. Pai, J. A. Taylor The optical transmission through a periodical array of subwavelength apertures in a metal film can be extraordinarily high due to resonance of the incident light with surface excitations, accompanied by dramatic enhancement of the local electromagnetic field on the metal surfaces. We have fabricated subwavelength slit arrays in two layers of metal. The two layers are positioned sufficiently close to each other so that the evanescent fields couple strongly at resonance. Depending on the lateral shift between the two layers, the transmission changes from near zero to a value that exceeds single layer transmission. Moreover, the phase delay of the transmitted light depends strongly on the lateral shift. We present both numerical simulations and experimental data to demonstrate that by tuning the lateral shift, an extra phase delay of $\pi $ can be introduced while the transmission remains near maximum. The controllable phase delay in bilayer subwavelength structures opens new capabilities that cannot be achieved with single layers. [Preview Abstract] |
Friday, March 14, 2008 8:36AM - 8:48AM |
X28.00004: Study of the absorption spectra of periodic hole arrays Dimitrios Koukis, Daniel Arenas, Sinan Selcuk, A.F. Hebard, D.B. Tanner, S.V. Shabanov The absorption of light by periodic hole arrays was studied for various open area fractions and wavelengths. We determined the absorption by measurements of the transmittance (T) and reflectance (R) at near normal incidence and setting the absorption as A = 1-R-T. The reflectance and transmittance were both measured, using a microscope photometer in the near infrared region and Bruker IFS 113v in the mid-infrared region. Periodic hole arrays are characterized by ``extraordinary'' transmittance (larger than the predictions of geometrical optics) at frequencies just below the onset of first order diffraction by the periodic array. The absorption maximum occurs at frequencies slightly larger than the transmittance maximum. The absorption results for the various open area fractions will be compared to theoretical predictions. [Preview Abstract] |
Friday, March 14, 2008 8:48AM - 9:00AM |
X28.00005: Steering and multiplexing subwavelength plasmon beams Vitalii Vlasko-Vlasov, Alexandra Imre, John Pearson, Jon Hiller, Ulrich Welp Arc shaped nanoslits in thin silver films are used as sources and lenses for generating sub-wavelength plasmon spots with high optical near-fields. We introduce a continuous phase shift along the nanoslits to achieve steering of the plasmon focus spot. It is experimentally shown that such a phase control allows to move the plasmon focus by micrometers with a nanometer precision and to launch it on separate 250 nm wide silver nanowires placed in the focal plane. Our nanostructures demonstrating scanning and multiplexing functionality show a feasibility of the nanoscale manipulation with optical fields. [Preview Abstract] |
Friday, March 14, 2008 9:00AM - 9:12AM |
X28.00006: Optical mapping of surface plasmon near-field spatial distribution in triangular silver nanoprisms Andrew Jones, Matthias Rang, Benjamin Wiley, Zhiyuan Li, Younan Xia, Markus Raschke Plasmonic metal nanostructures have attracted interest in diverse fields including biomolecular sensing and nano-photonics. To understand the correlation of the optical response with the shape and size of the structure, we optically stimulate localized surface plasmons on chemically prepared Ag triangular nanoprisms and utilize scattering-type Scanning Near-field Optical Microscopy (aSNOM) to map the optical near-field distribution with a spatial resolution down to 10nm. Using homodyne amplification allows for phase selective probing and identification of specific plasmon eigenmodes. For large triangles the superposition of several modes results in a complex distribution of the electric field whereas for smaller particles the distribution takes on a dipolar pattern. [Preview Abstract] |
Friday, March 14, 2008 9:12AM - 9:24AM |
X28.00007: Photonic delocalization and optical propagation in one-dimensional random n-mer dielectric systems Ruwen Peng, Zeng Zhao, Feng Gao, Lushuai Cao, De Li, Zhan Wang, Xiping Hao, Mu Wang We have both theoretically and experimentally investigated the propagation of electromagnetic waves in a one-dimensional random n-mer(RN) dielectric system. Due to the positional correlation in the RN structure, the localization- delocalization transitions of photons happen at expected frequencies of photons. Multiple resonant transmissions are found in the photonic band gap. At each resonant mode, zero- Lyapunov exponent and undecayed field distribution of electromagnetic waves have been found through the whole system. Furthermore, the channel is opened for photonic transport at the resonant frequency, and the density of states of photons increases step by step as frequency increases. The theoretical results are experimentally demonstrated in RN dielectric multilayer films of SiO2/TiO2 for visible and near infrared light. [Preview Abstract] |
Friday, March 14, 2008 9:24AM - 9:36AM |
X28.00008: Spontaneous quantum condensation in an optically-pumped microcavity far from equilibrium Paul Eastham, Richard Phillips We propose and analyze a method for creating highly non-equilibrium quantum condensates from excitons and photons in a semiconductor microcavity on timescales shorter than any thermalization times. In a theoretical study of microcavity dynamics we show that a tailored optical pulse can directly create a supercooled exciton population by an analogue of adiabatic rapid passage. This state involves no macroscopic occupations and is thus not a condensate. At later times, however, it spontaneously develops into a quantum condensate far from thermal equilibrium. This class of condensates encompasses phenomena similar to superradiance and lasing, but also includes states which give access to non-equilibrium Bose condensation in a solid-state system. [Preview Abstract] |
Friday, March 14, 2008 9:36AM - 9:48AM |
X28.00009: Random Laser Emission from ZnO Nanocomposite Hybrids A. Stassinopoulos, S. H. Anastasiadis, D. G. Papazoglou, D. Anglos, D. Tsagarakis, R. N. Das, E. P. Giannelis Highly scattering hybrid structures are produced either by incorporating ZnO nanoparticles in inert polymeric or inorganic sol-gel matrices or by depositing them on flexible substrates. All structures exhibit intense laser-like emission upon optical pumping. The ZnO particles provide both the gain and the strong scattering power, which lead to photon localization due to multiple scattering. The polymer matrix offers ease of material fabrication and processability while the elastic substrate offers flexibility in view of potential applications. Excitation of the hybrids by laser pulses shows threshold behavior demonstrated by a dramatic increase in the emitted light intensity and significant spectral and temporal narrowing. We study the influence of pump pulse duration and sample temperature on the random laser efficiency whereas we measure the coherence length of the emission. Nanocomposite fabrication issues and pumping conditions are varied aiming at performance optimization and, thus, potential use of such materials in future light emission devices. Sponsored by the Greek GSRT, by NATOs Scientific Affairs Division and by the EU. [Preview Abstract] |
Friday, March 14, 2008 9:48AM - 10:00AM |
X28.00010: Exciton energy spectra and optical-transition probabilities in InGaAs/GaAs ring-like nanostructures: Shape effects V.M. Fomin, V.N. Gladilin, J.T. Devreese, N.A.J.M. Kleemans, P.M. Koenraad We analyze the energy spectrum of an exciton and optical-transition probabilities for a model of self-assembled InGaAs/GaAs ring-like nanostructures, which is based on our X-STM data. We calculate the probabilities of optical transitions between the exciton vacuum and one-exciton states in the ring-like nanostructures. Spectral distributions of these probabilities as a function of the applied magnetic field are characterized by rich patterns, which significantly depend on shape, size and composition. Our analysis of the photoluminescence spectrum, observed in magnetic fields up to 30 T, implies a clear anisotropy of the measured nanostructures. For those anisotropic nanostructures, a smooth behavior of the exciton ground state energy as a function of the magnetic field is found in agreement with the experiment. We acknowledge collaboration with H. C. M. van Genuchten and M. Bozkurt. [Preview Abstract] |
Friday, March 14, 2008 10:00AM - 10:12AM |
X28.00011: Collective Plasmon Resonances and Their Influence on Metallic Nanostructures Ping Chu, Douglas L. Mills We present theoretical studies of the influence of collective plasmon resonances and their influence on enhanced fields, laser induced forces and related issues in selected examples of metallic nanostructures. Our new calculations focus on two nearby dissimilar nanospheres, and on nanospheres near a planar substrate. We show that when the response of two dissimilar spheres is compared to that of two isolated spheres, breakdown of a selection rule greatly increases the spectral range over which laser fields may couple to collective plasmons. We shall illustrate this with several selected examples. Collective plasmons also influence zero point fluctuations in the electric field near nanostructures; these produce non radiative transitions and energy level shifts within nearby molecules[1]. We shall present studies of the spatial distribution and frequency spectra of plasmon enhanced zero point fluctuations, with the near vicinity of STM tips in mind. [1] D. L. Mills, J. X. Cao and R. Wu, Phys. Rev B75, 214404, (2007). [Preview Abstract] |
Friday, March 14, 2008 10:12AM - 10:24AM |
X28.00012: Probing Bright and Dark Surface Plasmon Modes in Au Nanoparticles Using a Fast Electron Beam Ming-Wen Chu, Viktor Myroshnychenko, F. Javier Garc\'Ia de Abajo, Cheng Hsuan Chen We have studied the surface plasmons (SPs) of individual and coupled Au nanoparticles (NPs) with various sizes and shapes by electron energy-loss spectroscopy (EELS) using a 2-nm monochromatized fast electron beam in a scanning transmission electron microscope (STEM). EELS spectra were investigated with the beam in grazing incidence, the optical near-field setup, and \textit{bright} SP modes (visible by light) were identified in both individual, coupled NPs ranging from near-IR to visible regimes. In an individual long rod with an aspect ratio of $\sim $6, a \textit{dark} SP mode invisible by light was surprisingly characterized, supported by calculations of the macroscopic dielectric responses. With the NPs coupling, rich bright, dark SP modes emerge and the suppression of one mode over the other is dictated by the beam position when approaching a geometrically centered site. The electron scattering geometry thus plays the role the SP-mode selection, never documented before. [Preview Abstract] |
Friday, March 14, 2008 10:24AM - 10:36AM |
X28.00013: Quantum confined Stark effect in organic fluorophores. Xihong Peng, John Anderson, Gary Tepper, Supriyo Bandyopadhyay, Saroj Nayak Fluorescent molecules have widely been used to detect and visualize structure and processes in biological samples due to its extraordinary sensitivity. However, the emission spectra of flurophores are usually broad and the accurate identification is difficult. Recently, experiments show that energy shifts by Stark effect can be used to aid the identification of organic molecules [1]. Stark effect originates from the shifting/splitting of energy levels when a molecule is under an external electric field, which shows a shift/splitting of a peak in absorption/emission spectra. The size of the shift depends on the magnitude of the external field and the molecular structure. In this talk we will show our theoretical study of the peak shifts on emission spectra for a series of organic fluorophores such as tyrosine, tryptophan, rhodamine123 and coumarin314 using density functional theory. We find that a particular peak shift is determined by the local dipole moments of molecular orbitals rather than the global dipole moment of the molecule. These molecular-specific shifts in emission spectra may enable to improve molecular identification in biosensors. Our results will be compared with experimental data. [1]Unpublished, S. Sarkar, B. Kanchibotla, S. Bandyopadhyay, G. Tepper, J. Edwards, J. Anderson, and R. Kessick. [Preview Abstract] |
Friday, March 14, 2008 10:36AM - 10:48AM |
X28.00014: Effects of electron heating on femtosecond laser-induced coherent acoustic phonons Jincheng Wang, Chunlei Guo In this work, we employ a surface plasmon technique to resolve the dynamics of femtosecond laser-induced coherent acoustic phonons in noble metals. Clear acoustic oscillations are observed in our experiments. We further find that the initial phase decreases linearly with pump fluence. Our model calculations show that the hot electrons instantaneously excited by femtosecond pulses contributes to the generation of coherent acoustic phonons in metals. [Preview Abstract] |
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