The spatial and spectral responses of the plasmonic fields induced in the gap of 3-D nanoshell dimers of gold and silver are comprehensively investigated and compared via theory and simulation using the multipole expansion (ME) and the finite element method (FEM) in COMSOL, respectively. The E-field in the dimer gap was evaluated and compared as a function of shell thickness, interparticle distance, and size. The E-field increased with decreasing shell thickness, decreasing interparticle distance, and increasing size, with the error between the two methods ranging from 1 to 10%, depending on the specific combination of these three variables. This error increases several fold with increasing dimer size, as the quasi-static approximation breaks down. A consistent overestimation of the plasmon's fwhm and red shifting of the plasmon peak occurs with FEM, relative to ME, and it increases with decreasing shell thickness and interparticle distance. The size effect that arises from surface scattering of electrons is addressed and shown to be especially prominent for thin shells, for which significant damping, broadening, and shifting of the plasmon band is observed; the size effect also affects large nanoshell dimers, depending on their relative shell thickness, but to a lesser extent. This study demonstrates that COMSOL is a promising simulation environment to quantitatively investigate nanoscale electromagnetics for the modeling and designing of surface-enhanced Raman scattering (SERS) substrates.
"Aizpurura  used a Boundary- Charge Method to compute EEL spectra of inhomogeneous wedges, coupled parallel cylinders, coupled spheres, and toroidal surfaces. Khoury et al.  compared the results of a Finite Element Method (FEM)  against Mie theory  for silver and gold nanoshell dimers. Geuquet and Henrard  adapted the well-known Discrete Dipole Approximation (DDA)   to compute EEL spectra of silver nanoprisms. "
[Show abstract][Hide abstract] ABSTRACT: We numerically simulate low-loss Electron Energy Loss Spectroscopy (EELS) of isolated spheroidal nanoparticles, using an electromagnetic model based on a Generalized Multipole Technique (GMT). The GMT is fast and accurate, and, in principle, flexible regarding nanoparticle shape and the incident electron beam. The implemented method is validated against reference analytical and numerical methods for plane-wave scattering by spherical and spheroidal nanoparticles. Also, simulated electron energy loss (EEL) spectra of spherical and spheroidal nanoparticles are compared to available analytical and numerical solutions. An EEL spectrum is predicted numerically for a prolate spheroidal aluminum nanoparticle. The presented method is the basis for a powerful tool for the computation, analysis and interpretation of EEL spectra of general geometric configurations.
[Show abstract][Hide abstract] ABSTRACT: We present three important extensions of the plasmon hybridization (PH) method: a generalization of the method to include
realistic non-Drude dielectric permittivities for metals, the development of an algorithm for the calculation of plasmon-induced
electric field enhancements, and the extension of the PH method to the modeling of plasmonic Fano resonances. We illustrate
these developments with an application to a silver nanosphere dimer and a symmetric silver nanosphere heptamer.
Keywordsplasmon hybridization-plasmon-Fano resonances-nanoparticle
Chinese Science Bulletin 08/2010; 55(24):2629-2634. DOI:10.1007/s11434-010-4070-y · 1.58 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report on a new analytical approach to intracellular chemical sensing that utilizes a surface-enhanced Raman spectroscopy (SERS)-enabled nanopipette. The probe is comprised of a glass capillary with a 100-500 nm tip coated with gold nanoparticles. The fixed geometry of the gold nanoparticles allows us to overcome the limitations of the traditional approach for intracellular SERS using metal colloids. We demonstrate that the SERS-enabled nanopipettes can be used for in situ analysis of living cell function in real time. In addition, SERS functionality of these probes allows tracking of their localization in a cell. The developed probes can also be applied for highly sensitive chemical analysis of nanoliter volumes of chemicals in a variety of environmental and analytical applications.
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