Jason M. Montgomery

Molded plasmonic crystals for detecting and spatially imaging surface bound species by surface-enhanced Raman scattering

This report introduces a type of plasmonic crystal that consists of metal coated nanostructures of relief molded on a polymer film as a substrate for surface-enhanced Raman scattering (SERS). Such crystals exhibit SERS enhancement factors of ∼105, over large areas and with sufficiently high levels of uniformity for precise two-dimensional Raman mapping of surface bound monolayers. The ease of fabrication together with the high sensitivities and spatial resolution that can be achieved suggests an attractive route to SERS substrates for portable chemical warfare agent detection, environmental monitors, noninvasive imaging of biomolecules, and other applications.

SERS enhancements via periodic arrays of gold nanoparticles on silver film structures.

We discuss surface enhanced Raman spectroscopy (SERS) structures aimed at providing robust and reproducible enhancements. The structures involve periodic arrays of gold nanospheres near silver film structures that may also be patterned. They enable one to excite Bloch wave surface plasmon polaritons (SPPs) that can also couple to local surface plasmons (LSPs) of the nanospheres, leading to the possibility of multiplicative enhancements. If the magnitude of the average electric field, /E/, between the particles is enhanced by g such that /E/ = g/E(0)/, /E(0)/ being the incident field, realistic finite-difference time-domain simulations show that under favorable circumstances g approximately equal 0.6 g(SPP) g(LSP), where g(SPP) and g(LSP) are enhancement factors associated with the individual components. SERS enhancements for the structures can be as high as O(g(4)) = 10(8).

Theory and modeling of light interactions with metallic nanostructures

Metallic nanostructures such as systems containing metal nanoparticles or nanostructured metal films are intriguing systems of much current interest. Surface plasmons, i.e., special electronic excitations near the metallic surfaces, can then be excited in these systems. Surface plasmons can be intense and localized, and correctly describing their behavior in complex systems can require numerically rigorous modeling techniques. The finite-difference time-domain (FDTD) method is one such technique. This review discusses results obtained mostly with the FDTD method concerning (i) local surface plasmon excitations of metal nanoparticles, (ii) surface plasmon polariton propagation on layered structures, (ii) and periodic hole arrays in metal films.

Plasmonic electromagnetic hot spots temporally addressed by photoinduced molecular displacement.

We report the observation of temporally varying electromagnetic hot spots in plasmonic nanostructures. Changes in the field amplitude, position, and spatial features are induced by embedding plasmonic silver nanorods in the photoresponsive azo-polymer. This polymer undergoes cis-trans isomerization and wormlike transport within resonant optical fields, producing a time-varying local dielectric environment that alters the locations where electromagnetic hot spots are produced. Finite-difference time-domain and Monte Carlo simulations that model the induced field and corresponding material response are presented to aid in the interpretation of the experimental results. Evidence for propagating plasmons induced at the ends of the rods is also presented.

Large-scale electromagnetic modelings based on high-order methods: Nanoscience applications

This paper presents large-scale computations and theoretical or computational aspects of the spectral element methods for solving Maxwells equations that have potential applications in nanoscience for surface-enhanced Raman scattering (SERS) and solar cell devices. We study the surface-enhanced electromagnetic fields near the surface of metallic nanoparticles using spectral element discontinuous Galerkin method. We solve Maxwells equations in time-domain and provide accuracy and efficiency of our method compared to the conventional finite difference method. We demonstrate light transmission properties for nanoslab and nanoslits, and time-averaged electric fields over the cross sections of nanoholes in a hexagonal array.