Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session P24: Focus Session: Optical Properties of Nanostructures V: Plasmonics and Metallic Nanostructures |
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Sponsoring Units: DMP Chair: Nicholas Fang, University of Illinois Room: Morial Convention Center 216 |
Wednesday, March 12, 2008 8:00AM - 8:12AM |
P24.00001: Calculations of second harmonic generation by nano-particles or holes William Schaich We are setting up finite-difference time-domain (fdtd) calculations of second harmonic generation (shg) by metallic nano-particles or at nano-holes in metallic films. This generation is driven by first order fields at the metal surfaces, using the phenomenological a and b parameters that have been used to describe shg at planar jellium-metal surfaces. Our interest is in locating and understanding the occurrence of resonances and hot-spots for shg. [Preview Abstract] |
Wednesday, March 12, 2008 8:12AM - 8:24AM |
P24.00002: Plasmonic bonding and anti-bonding forces in a bisphere Tsz Fai (Jack) Ng, C.T. Chan By exciting the surface plasmon resonance of a pair of nanoparticles using intense laser illumination, one can exert huge optical forces on the nanoparticles. We calculate such resonant optical force using a multiple scattering and Maxwell stress tensor formalism, which is ``exact'' within the classical electrodynamics. It is shown that the full electrodynamic calculation can give results that differ significantly from those obtained by the quasi-static approximation. As the pair of nanoparticles approach each other, the individual particle's plasmonic modes hybridize and split into bonding and anti-bonding modes, which induced attraction and repulsion respectively. At very small separations, the bonding (anti-bonding) modes are forced to curve downward (upward) in frequency significantly, resulting in the formation of a low frequency attractive (high frequency repulsive) band. Consequently, a low frequency laser illumination will induce strong attraction, promoting particle-clustering, and a high frequency illumination will induce strong repulsion, preventing particle aggregation. With high intensity, these resonant forces can dominate over the other relevant forces, including the van der Waals force, when the separation between the particles is several nanometers. [Preview Abstract] |
Wednesday, March 12, 2008 8:24AM - 8:36AM |
P24.00003: Surface-enhanced Raman Scattering from Virus-like Particle Crystals Christopher DuFort, Bogdan Dragnea Recently, a method for the encapsidation of gold nanoparticules by an icosahedral virus protein coat, termed a virus-like particle (VLP), has been developed. Of particular interest is in observing their spectroscopic properties upon arrangement into a three-dimensional crystal lattice. Here we present the surface-enhanced Raman scattering spectrum of such an assembly. This is made possible by the plasmonic coupling of adjacent gold nanoparticules when excited near their plasmon resonant frequency. To determine whether the SERS effect is arising from isolated hot spots or a large number of junctions acting in unison we employed scanning confocal Raman spectroscopy. This seems to indicate the latter, as a uniform Raman intensity is observed across entire crystals. [Preview Abstract] |
Wednesday, March 12, 2008 8:36AM - 8:48AM |
P24.00004: The effects of nanoparticle spacing on second-harmonic generation from gold nano-dimers Davon W. Ferrara, Kevin A. Tetz, Matthew D. McMahon, Richard F. Haglund, Jr. Second-harmonic generation (SHG) is an important signature of electron dynamics in nanoparticles (NPs) as well as a sensitive probe of surface effects. In the gap between closely spaced pairs of NPs, or nanodimers (NDs), localized electromagnetic field energy creates a hot spot that has been shown to affect SHG from asymmetric NDs. We will present new experimental results demonstrating the role that gap size and field localization plays in SHG from centrosymmetric arrays of gold NDs. Using standard electron-beam lithography techniques, NPs were made 20 nm in height with varying areal aspect ratios. In the ND arrays, symmetry forbids SHG in the forward direction, but not at larger angles. Our experiments indicate suppression in SHG intensity with decreasing gap size and evidence of stronger long range interactions between NPs with separation over 200 nm. Finite-difference time-domain simulations were also performed in order to correlate field localization with SHG. Our simulations show a strong dependence on the polarization of incident light. [Preview Abstract] |
Wednesday, March 12, 2008 8:48AM - 9:00AM |
P24.00005: Optical Imaging Properties of Metal Nanoparticle Chains David Citrin Chains of noncontacting noble-metal nanoparticles are known to support coupled plasmonic-electromagnetic modes known as plasmon polaritons, in which those polarized perpendicular to the chain axis exhibit group and phase velocity in opposite directions. This in turn has attracted interest in nanoparticle chains and arrays as left-handed materials for optical applications. In this contribution, I discuss recent work in my group on the imaging properties of nanoparticle chains. In particular, I present work that demonstrates theoretically the focusing properties of nanoparticle chains. I further discuss possible applications in near-field optics. [Preview Abstract] |
Wednesday, March 12, 2008 9:00AM - 9:12AM |
P24.00006: Plasmonic superfocusing on metallic tips for near-field optical imaging and spectroscopy Catalin C. Neacsu, Rob Olmon, Samuel Berweger, Alexandria Kappus, Friedrich Kirchner, Claus Ropers, Lax Saraf, Markus B. Raschke Realization of localized light sources through nonlocal excitation is important in the context of plasmon photonics, molecular sensing, and in particular near-field optical techniques. Here, the efficient conversion of propagating surface plasmons, launched on the shaft of a scanning probe tip, into localized plasmon at the apex provides a true nanoconfined light source. Focused ion beam milling is used to generate periodic surface nanostructures on the tip shaft that allow for tailoring the plasmon excitation. Using ultrashort visible and mid-IR transients the dynamics of the propagation and subsequent scattered emission is characterized. The strong field enhancement and spatial field confinement at the apex is demonstrated studying the coupling of the tip in near-field interaction with a flat sample surface. It is used in scattering near-field spectroscopic imaging (s-SNOM) to probe surface nanostructures~with spatial resolution down to 10 nm. [Preview Abstract] |
Wednesday, March 12, 2008 9:12AM - 9:24AM |
P24.00007: Novel properties of nanostructured metal particles and films Shengli Zou Using electromagnetic dynamics, we simulate the extinction spectra and enhanced electric fields of nanostructured metal nanoparticles and films. Their sensing and waveguide applications will be discussed. The sensing of molecules is achieved by the shift of the plasmon resonance wavelength of nanoparticles or enhanced Raman scattering or fluorescence signals, which are due to the enhanced local electric fields near or far away from the metal surface. The waveguide is achieved by the electromagnetic coupling in a one dimensional particle chain or a perforated metal film. [Preview Abstract] |
Wednesday, March 12, 2008 9:24AM - 9:36AM |
P24.00008: Resonance of metallic wire structures Lei Zhou, Y. Zhang, Siu Tat Chui Metallic wire structures form a common class of physical systems. We illustrate how to understand the general physics of the wire systems with a specific example, the split ring resonantor. We derived simple polynomial equations to determine the entire resonance spectra of split ring structures, which can be analytically solved in the limit of narrow wires. A resonance spectrum very similar to that of a straight wire is obtained. For double stacking split rings made with flat wires, we showed that the resonance frequency depends linearly on the ring-ring separation. In particular, we found that the wavelength of lowest resonance mode can be made as large as $10^5$ the geometrical size of the ring for realistic experimental conditions, whereas for current systems this ratio is of the order of 10. Finite-difference-time-domain simulations on realistic structures verified the analytic predictions. [Preview Abstract] |
Wednesday, March 12, 2008 9:36AM - 9:48AM |
P24.00009: Fabrication of Plasmonic Optical Probe and Its Characterization Seong Soo Choi, D.W. Kim, Vinayah Jha, O. Suwal, M.J. Park Recently, there have been tremendous interests about the nano-structured optical probe using surface plasmon polariton due to possible applications of the next generation local communication devices and nano-bio sensor technology. The nano-size metallic apertures such as metal-coated fiber probe and microfabricated pyramidal probe, have shortcomings of very low output intensities. With periodic groove or defects near the aperture on the microfabricated pyramidal probe, the huge output intensity enhancement has been reported [1]. In this talk, the fabrication with nano-flowers including metallic scattering centers around the nano-size aperture and its optical characterization of the pyramidal metallic probe will be presented. References: [1] The effect of groove shape on light transmission, S.S. Choi, etc, 3$^{rd}$ International Conference on Surface Plasmon Photonics, June 17-22, Dijon, France. [Preview Abstract] |
Wednesday, March 12, 2008 9:48AM - 10:00AM |
P24.00010: Inter-particle coupling and polarizability of silver nanoparticle dimers Ke Zhao, Claudia Troparevsky, Adolfo Eguiluz, Zhenyu Zhang Using a real-space implementation of density-functional theory, we investigate systematically the electronic/chemical coupling of two silver nanoparticles of varying sizes. The nanoparticles are allowed to approach each other along two distinct directions defined by, respectively, maximum and minimum static polarizabilities. We show that, as the inter-particle separation decreases, the static polarizability of the dimer shows signatures of crossover to a strong-coupling regime. Moreover, we analyze the connection between the crossover from weak to strong coupling regimes of the nanoparticles and the electron density overlap from the states contributed by the individual nanoparticles. The significance of these results will be discussed in connection with the prevailing theories of the electromagnetic enhancement of surface-enhanced Raman scattering. [Preview Abstract] |
Wednesday, March 12, 2008 10:00AM - 10:12AM |
P24.00011: Enhancement of Light Transmission through Bull's Eye Structures Sinan Selcuk, Daniel Arenas, David B. Tanner, Arthur F. Hebard Optical transmission of a single hole in a metal film surrounded by concentric surface grooves is shown to have an enhanced transmission. We fabricated these structures in silver films which are thin enough to let light through without a center hole. We have measured the optical transmission and reflection in visible to near infrared spectrum observing enhanced transmission scaling with groove periodicity. Opening a hole in the center gives rise to destructive interference between the light passing through the structure and the light passing through the hole. We will discuss the mechanisms behind light transmission for the bullseye structure for varying hole size, groove periodicity, groove depth and the metal thickness. [Preview Abstract] |
Wednesday, March 12, 2008 10:12AM - 10:24AM |
P24.00012: Fluorescence enhancement from nominally flat surfaces Shy-Hauh Guo, Hung-Chih Kan, Ray Phaneuf We report on experimental investigations of fluorescence enhancement from nominally flat silver and silicon substrates, in the presence of an oxide spacer layer. By varying the thickness of the oxide layer to change the spacing between fluorophores and the substrate, we find that the relative fluorescent intensity measured above Ag vs. Si substrates oscillates, indicating a resonant effect. We investigate the effect of nanoscale roughness on the observed fluorescent enhancement. [Preview Abstract] |
Wednesday, March 12, 2008 10:24AM - 10:36AM |
P24.00013: Anisotropic Light Scattering from Ferrofluids Corneliu Rablau, Prem Vaishnava, Ratna Naik, Gavin Lawes, Ron Tackett, C. Sudakar We have investigated the light scattering in DC magnetic fields from aqueous suspensions of Fe$_{3}$O$_{4}$ nanoparticles coated with tetra methyl ammonium hydroxide and $\gamma $-Fe$_{2}$O$_{3}$ nanoparticles embedded in alginate hydrogel. For Fe$_{3}$O$_{4}$ ferrofluid, anomalous light scattering behavior was observed when light propagated both parallel and perpendicular to the magnetic fields. This behavior is attributed to the alignment and aggregation of the nanoparticles in chain-like structures. A very different light scattering behavior was observed for $\gamma $-Fe$_{2}$O$_{3}$ alginate sample where, under the similar conditions, the application of the magnetic field produced no structured change in scattering. We attribute this difference to the absence of chain-like structures and constrained mobility of iron nanoparticles in the alginate sample. The observation is in agreement with our relaxation and dissipative heating results$^{1}$ where both samples exhibited Neel relaxation but only the Fe$_{3}$O$_{4}$ ferrofluid showed Brownian relaxation. The results suggest that Brownian relaxation and nanoparticle mobility are important for producing non-linear light scattering in such systems. $^{1}$P.P. Vaishnava, R. Tackett, A. Dixit, C. Sudakar, R. Naik, and G. Lawes, J. Appl. Phys. \textbf{102}, 063914 (2007). [Preview Abstract] |
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