Geometry-dependent plasmon resonances of metallic nanostructures for enhancement of localized electromagnetic fields around the nanostructures

Abstract

This paper describes theoretical and experimental evaluations of electromagnetic fields around metallic nanostructures, such as nanorods, nano-pillars, and a collection of nanorods separated by nano-scale distances. Nanostructures having different sizes and shapes were evaluated. The spacing between nanorods and elliptical nanopillars was varied such that the effect of nanoparticle spacing on the electromagnetic fields in the regions between the nanostructures could be studied. Gold was the metal employed in our work as it demonstrates substantial plasmon excitation and is chemically stable. Calculations of the electromagnetic fields in the vicinity of the different metallic nanostructures were made by employing Finite Difference Time Domain (FDTD). Refractive index of the media surrounding the nanostructures was varied for these calculations. These calculations were carried out at different wavelengths in the visible and near-infrared spectral regimes. In order to fabricate these nanostructures on silica substrates, focused ion beam (FIB) milling was employed. These structures were fabricated on gold-coated planar silica and mica substrates and tips of four mode and multimode optical fibers. In our experimental evaluations of the different metallic nanostructures, surface enhanced Raman scattering (SERS) signals from the different metallic nanostructures were obtained and were correlated to the spacing distance between the different metallic nanostructures.