ANALYZING THE CONFINEMENT AND ENHANCEMENT OF HOT SPOTS IN PLASMONIC NANOPARTICLE PAIRS,

EDIARDO M. PERASSI; LUIS R. CANALI; EDUARDO A. CORONADO

Valparaiso

Congreso; Tercera Reunión, SOLIDOS 2009; 2009

UNIVERSIDAD TECNICA FEDERICO SANTAMARIA

Noble metal nanoparticles (NPs) exhibit a variety of optical phenomenon related to the size and shape dependent surface plasmon resonances that can be excited by electromagnetic fields. Such optical phenomena are able to produce large scattering cross sections at specific wavelengths as well as strongly confined and enhanced electromagnetic fields in spatial regions usuallycalled Hot Spots (HS). HS are the core of all plasmon enhanced spectroscopies including Surface-Enhanced Raman Scattering (SERS), Tip-Enhanced Raman Spectroscopy (TERS) which have enabled the detection of single molecules. It is therefore of great importance to be able to determine accurately the electromagnetic field enhancement as wellas its degree of localization inside a HS, both from basic science and for applications in plasmonic devices. In a previous work we have developed a quantitative approach [6] to account for the degree of convergence, confinement and enhancement of electromagnetic fields generated in single plasmonic NPs. The approach is based on computing the variation of the volume trapped (VT ) between a constant  surface around a metal NP and the nanoparticle surface boundary as a function of the enhancement itself. This variation of the trapped volume (VTV) allow us to test the convergence of the electrodynamic calculation and could be fitted very accurately to an analytical expression of VT vs . Using this expression, the mean field enhancement within a trapped volume outside the NP as well as the degree of localization and spreading of the HS on 3D space could be determined. In the present work we have extended this approach to more complex nanostructures, in particular for "a pair of two plasmonic Nps", a system of great interest because of its potential to produce enormous. The calculations were performed using the DDA method for two representative nanoparticle pairs: a system of two spheres and bowtie nano-antennas separated a few nanometers from each other.