Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session A23: Plasmons and Optical Absorption |
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Sponsoring Units: DCMP Chair: David Singh, Oak Ridge National Laboratory Room: 325 |
Monday, March 16, 2009 8:00AM - 8:12AM |
A23.00001: Ternary cobalt spinel oxides for solar driven hydrogen production: Theory and experiment Aron Walsh, Kwang-Soon Ahn, Sudhakar Shet, Muhammad N. Huda, Todd Deutsch, Heli Wang, John A. Turner, Yanfa Yan, Mowafak M. Al-Jassim, Su-Huai Wei Discovery of a chemically stable, light absorbing and conductive metal oxide with band edges aligned to water redox potentials has been a goal of physical scientists for the past forty years. Despite an immense amount of effort, no solution has been uncovered. We will present the results of our combined theoretical and experimental exploration of a series of unconventional ternary cobalt spinel oxides, which offer chemical functionality through substitution on the tetrahedral spinel A site. First-principles predictions of the substitution of group 13 cations (Al, Ga, In) in Co$_3$O$_4$ to form a series of homologous CoX$_2$O$_4$ spinel compounds are combined with experimental synthesis and photoelectrochemical characterization. Ultimately, while tunable band gaps in the visible range can be obtained, the material performance is limited by poor carrier transport properties associated with small polarons. Future design pathways for metal oxide exploration will be briefly discussed. [Preview Abstract] |
Monday, March 16, 2009 8:12AM - 8:24AM |
A23.00002: Multiple electron generation in a sea of electronic states Wayne Witzel, Andrew Shabaev, Alexander Efros, Carl Hellberg, Jacobs Verne In traditional bulk semiconductor photovoltaics (PVs), each photon may excite a single electron-hole, wasting excess energy beyond the band-gap as heat. In nanocrystals, multiple excitons can be generated from a single photon, enhancing the PV current. Multiple electron generation (MEG) may result from Coulombic interactions of the confined electrons. Previous investigations have been based on incomplete or over-simplified electronic-state representations. We present results of quantum simulations that include hundreds of thousands of configuration states and show how the complex dynamics, even in a closed electronic system, yields a saturated MEG effect on a femtosecond timescale. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Monday, March 16, 2009 8:24AM - 8:36AM |
A23.00003: Quantum confined stark effect in non-identical InAs/GaAs coupled quantum dots: Dependence on vertical electrical field Muhammad Usman, Gerhard Klimeck InAs/GaAs coupled quantum dot (QDs) have gained much attention for optical and quantum computing applications. Due to strain, originating from assembly of lattice- mismatched semiconductors, quantum dot tend to grow in the vertical direction. These stacked QDs are strongly coupled through strain field, which is atomistically inhomogeneous and penetrates deep into GaAs buffer layer surrounding the dots. Piezoelectric field must be taken into account to properly model the experimentally observed symmetry breaking and a global shift in the energy spectra of the system. Vertical electrical field applied in the growth direction results in the red shift of emission spectra due to the quantum confined stark effect. Previous studies are based on kp method that ignore the crystal symmetry, optical anisotropy and piezoelectricity effects. In this work, we apply a twenty band sp$^{3}$d$^{5}$s* atomistic tight binding model to study the experimentally observed red shift of emission spectra resulting from an applied electrical field. We quantitatively compare the results for coupled QDs with the results for single QD. [Preview Abstract] |
Monday, March 16, 2009 8:36AM - 8:48AM |
A23.00004: Experimental Kataura plot from individual Single-Wall Carbon nanotubes on silicon substrate. Ya-Ping Hsieh, Mario Hofmann, Chi-Te Liang, Mildred S. Dresselhaus, Jing Kong The dependence of Raman scattering of individual carbon nanotubes on excitation energy was investigated. For this carbon nanotubes were grown on Silicon substrate and their Raman spectra were analyzed for a multitude of different laser excitation wavelength. Resonance windows for several tubes within one family were measured to obtain the energy of maximum intensity of the RBM feature. By carefully calibrating these RBM peak positions, this experimental data can generate an experimental Kataura plot, which was compared to the theoretical prediction. Finally, a relation between RBM frequency and diameter was obtained based on the experimental Kataura plot. These results will improve the chirality assignment of carbon nanotubes grown on silicon substrate. [Preview Abstract] |
Monday, March 16, 2009 8:48AM - 9:00AM |
A23.00005: Effect of Multi-Resonance Subband Structure on the Kerr Nonlinearity of Quantum-Cascade Lasers Jing Bai This work focuses on the investigation of the optical Kerr lensing effect in quantum-cascade lasers with multiple resonance levels. The Kerr refractive index $n_{2}$ is obtained through the third-order susceptibility at the fundamental frequency \textit{$\chi $}$^{(3)}$(\textit{ $\omega $}). Resonant two-photon processes are found to have almost equal contributions to \textit{$\chi $}$^{(3)}$(\textit{$\omega $}) as the single-photon processes, which result in the predicted enhancement of the positive $n_{2}$, and thus may enhance mode-locking of quantum-cascade lasers. Moreover, an isospectral optimization strategy for further improving $n_{2}$ through the band-structure design is also demonstrated, in order to boost the multimode performance of quantum-cascade lasers. Simulation results show that the optimized stepwise multiple-quantum-well structure has a twofold enhancement on $n_{2}$ over the original flat quantum-well structure. This leads to a refractive-index change $\Delta n$ of about 0.01, which is at the upper bound of those reported for typical Kerr medium. This stronger Kerr refractive index may be important for quantum-cascade lasers ultimately to demonstrate self-mode-locking. [Preview Abstract] |
Monday, March 16, 2009 9:00AM - 9:12AM |
A23.00006: Anisotropic Electronic Screening due to Fermi Surface Nesting in Graphite James Reed, Young Il Joe, Diego Casa, Thomas Gog, Y. Q. Cai, Peter Abbamonte We used inelastic X-ray scattering to measure the imaginary part of the density-density Green's function, Im[$\chi(\vec k;\omega)$], of a single crystal graphite sample along six direction in the Basal plane from [100] to [110]. To place Im[$\chi(\vec k;\omega)$] on an absolute scale we calculate a scaling coefficient using the optical sum rule. The real part of $\chi(\vec k;\omega)$ is calculated via the Kramers-Kronig transformation. We use an inversion algorithm to map the data into real space at various time intervals with attosecond time resolution. The images of the density response we produced show hexagonal anisotropy, which arises from scattering between the K and K' points of the Brillouin zone. Analysis of the data at $\omega=0$ provides us with the anisotripic induced electron density around a static impurity as function of distance. Integration of the local density around $\vec r=0$ gives the effective charge of the impurity from which we deduced the background dielectric constant, $\epsilon_{\infty}$, to be approximately 2.23. [Preview Abstract] |
Monday, March 16, 2009 9:12AM - 9:24AM |
A23.00007: Plasmons in the presence of Tamm-Shockley states with Rashba splitting at noble metal surfaces Abdel-Khalek Farid, Eugene Mishchenko Au(111) or similar noble metal surfaces feature Tamm-Shockley surface states that are known to possess considerable spin-orbit splitting of the Rashba type of order $\Delta=0.1$ eV. When interacting with an electromagnetic field such states are expected to have resonances when the frequency of the field is near the energy of the spin-orbit splitting $\Delta$. They originate from the intersubband transitions between spin-split subbands and can be observed in the frequency dependence of the surface impedance. Plasmons in thin metal films are gapless and can be strongly affected by these spin resonances, acquiring significant modification of the spectrum when it intersects the $\omega=\Delta$ line. Finally, an interesting demonstration of the intersubband resonances can be achieved when metal films are coated with ionic dielectrics that have a frequency of longitudinal/transverse optical phonons above/below $\Delta$. The dielectric function between the two optical phonon frequencies is negative which forbids propagation of conventional plasmon-polaritons. However, the presence of spin-orbit-split surface states allows plasmon-polaritons to exist in this otherwise forbidden range of frequencies. [Preview Abstract] |
Monday, March 16, 2009 9:24AM - 9:36AM |
A23.00008: Phases Shift in Sub-wavelength Plasmonic Hole on Thin Metal Film. Jun Xu, Hyungjin Ma, Nicholas X. Fang While recent study of extraordinary transmission of light through sub-wavelength plasmonic nanostructures shows promise of novel nanophotonic elements in sensing and display, the origin of such phenomena is still under hot debate. In this paper, we measured the phase delay of the squeezed light emerging from individual plasmonic holes. Near-field Scanning Optical Microscope (NSOM) has been used to measure the interference of transmitted and scattered light of an isolated sub-wavelength hole on thin metal film. Our results indicate that even with a 30nm perforated film, the observed phase shift can be as large as 300 degrees, well beyond the prediction from earlier theoretical models. Counter intuitively, the measured phase shift is sensitive to the wavelength, the film thickness but insensitive to hole diameter. Also, full scale simulation by COMSOL has been done to show the more detail features inside the metal film. Our study may provide new insight to compact and efficient optoelectronic devices. [Preview Abstract] |
Monday, March 16, 2009 9:36AM - 9:48AM |
A23.00009: Coupling between Surface Plasmon Resonance and electric current in Au stripes Miguel Angel Garcia, Aida Serrano, Jose de la Venta Surface Plasmon Resonance (SPR) is the most outstanding feature of noble metal films. SPR consists on a collective oscillation of the conduction electrons when excited optically in the appropriate geometrical and energy conditions. The electrical current passing trough the metal film involves also the movement of conduction electrons. Thus, coupling effects are expected between SPR and electrical resistivity. A modification of the SPR when a electrical current passes through the film, could allow the modulation of an optical signal by a electrical one. Similarly, when the film is illuminated at the SPR conditions, the oscillation of the conduction electrons and local heating can induce an enhancement of the electric resistivity that can be used to translate an optical signal into a electric one. Those effects could be useful in the development of new fast optoelectronic transducers. We present here results on Au stripes illuminated to induce the SPR while electric currents flow with different orientation with respect to the light polarization [Preview Abstract] |
Monday, March 16, 2009 9:48AM - 10:00AM |
A23.00010: Surface plasmon resonance enhanced binding of metal nanoparticles K.L. Chan, M.J. Zheng, K.W. Yu The interparticle force between metallic nanoparticles illuminated by laser light has been studied theoretically. When the distances between the particles are sufficiently small, the excitation of surface plasmon modes within these particles can lead to strongly enhanced laser fields. As a result, there are strongly enhanced light-induced binding forces between these nanoparticles. For physically realizable laser power, these forces can exceed the van der Waals forces by several orders of magnitude. In our theoretical calculations, we considered the interparticle force and potential between two approaching metal nanoparticles. The metal particles are routinely modelled as Drude metallic spheres, and the interparticle force has been captured conveniently by an approximate multiple image formula between two spheres. When the incident light frequency is near the surface plasmon resonant frequency, we find that the force varies nonmonotonically with the distance and a stable local minimum in the potential energy can be found, signifying a binding between the particles. On the experimental and technological side, these studies are also crucial to optical spectroscopy in the nanoscales. Work supported by the General Research Fund of the Hong Kong SAR Government. [1] J. P. Huang, K. W. Yu, G. Q. Gu Electrorotation of a pair of spherical particles, Phys. Rev. E, Vol. 65, art. no. 021401 (2002). [Preview Abstract] |
Monday, March 16, 2009 10:00AM - 10:12AM |
A23.00011: Giant Electric Field Generation in Nano-Metallic Cylinder Chains Due to Plasmon Propagation Angela Camacho, Juan Carlos Arias We present a study of the superficial plasmons propagation in a chain of nano-metalic cylinders by analyzing: size effect and coupling between the particles. Particularly, we focus on the main features of electric fields in the inter-cylinder regions due to their relationship with SERS(Surface-enhanced Raman Scattering). Giant electric fields have been observed in spherical nano-particles showing an enormous increasing of the cross section, which offers very interesting applications in molecular physics. We calculate the external radiation effect on chains of cylinders lateral and vertically coupled and examine the Plasmon formation in them. Specially, we study the Plasmon propagation depending on the particle size, the separation between them and the type of coupling. We find enhanced electric fields in the inter-particles regions showing the charge accumulation and border effects in cylinders, which are strongly dependent on the two above proposed parameters, and we also extend our results to possible Surface Enhanced Raman Scattering geometric effect to make a comparison with the spherical nano-particles. [Preview Abstract] |
Monday, March 16, 2009 10:12AM - 10:24AM |
A23.00012: Optical properties of medium size noble and transition metal nanoparticles Juan C. Idrobo, Sokrates T. Pantelides Using first-principles methods within time dependent density functional theory and the local density approximation (TDLDA) the absorption spectra of medium size ($\sim $20-80 atoms) silver, gold and copper nanoparticles have been calculated. The nanoparticles are fcc fragments with different aspect ratios. We find that in the case of Ag nanoparticles is well reproduced by classical electrodynamics theory based in Mie's formalism, using the dielectric function of bulk Ag and taking into account the nanoparticle shape. For the case of Cu and Au, there is a similarity in the overall features of the quantum mechanical and classical spectra, but no detailed agreement. We will discuss the role that the d-electrons among all the different elements and the surface states play in controlling the optical properties of the nanoparticles. This work was supported by GOALI NSF grant (DMR-0513048), DOE, the Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, and Alcoa Inc. [Preview Abstract] |
Monday, March 16, 2009 10:24AM - 10:36AM |
A23.00013: Electronic Coupling and Optimal Gap Size within a Metal Nanoparticle Dimer Ke Zhao, Claudia Troparevsky, Di Xiao, Adolfo Eguiluz, Zhenyu Zhang We study the electronic coupling between two metal nanoparticles using density functional theory methods. We show that a continuous change in the particle separation leads to an abrupt transition from strong to weak electronic coupling, which defines an optimal separation for the dimer. While in the weak-coupling regime the dimer behaves like isolated clusters, its crossing into the strong-coupling regime is signified by two distinct phenomena, namely, the onset of a net magnetic moment, and a maximum in the static polarizability. We also show that as the system switches over from strong to weak coupling regime, the response to an applied electric field is nonlinear even for very small fields. The strong dependence of the coupling on the atomic structure of the nanoparticles and their orientation is also discussed. Our study is expected to have an impact on a variety of systems composed of aggregates of nanoparticles. [Preview Abstract] |
Monday, March 16, 2009 10:36AM - 10:48AM |
A23.00014: Extraordinary Optical Transmission through Circular Nanotrenches in Ag Films Feng Wang, Min Xiao, Qihuo Wei This work reports studies on the extraordinary transmission of normally incident light through sub-wavelength circular nanotrenches in Ag films. The concentric periodic nanotrenches are perforated through 100nm thick Ag films by using focused-ion beam (FIB). Far-field transmission measurements show that under the illumination of linearly polarized white light, the transmitted light is not linearly polarized and exhibits broad-band enhanced transmission with the center wavelength varying with the periodicity of the trenches. These spectroscopic experimental results can be reproduced qualitatively through finite-difference time domain (FDTD) simulations. Especially, simulations show that the transmitted light is radially polarized at low frequencies, while azimuthally polarized at high frequencies. These interesting polarization statuses can be explained as a result of competition between transmission of s and p polarized light through periodic gratings of nanotrenches. [Preview Abstract] |
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