Modelling core-shell plasmonic nanoparticles as homogenous systems: An effective refractive index approach

Abstract

Core-shell plasmonic nanoparticles have attracted significant interest for use in a vast number of applications such as optoelectronics, solar energy, and drug delivery. However, modeling core-shell nanoparticles as two distinct regions, namely the core and the shell leads to computational complexity, especially in large systems. Additionally, most metallic plasmonic nanoparticles develop a self-limiting oxide shell, creating in effect, a metal-metal oxide core-shell system. Effective medium theories have emerged as a technique to study core-shell nanoparticles as a single homogenous system. However, current effective medium theories are limited due to their low accuracy, especially for larger core and shell thicknesses (>50nm). Here, we present a novel method that determines an effective refractive index enabling spherical core-shell nanoparticles, of varying core and shell radii and material composition, to be represented as a single homogenous nanoparticle; thus allowing for quick, efficient and simple calculations with accuracies similar to that obtained by using analytical solutions given by Mie Theory. This technique holds prospects to model the properties of core-shell nanoparticles for applications such as plasmonic enhanced solar cell simulations, for quantification of heat generated by plasmonic nanoparticles (thermoplasmonics) etc. This technique will hence enable rapid and accurate calculations of the optical properties of core-shell nanoparticles for a variety of technologies.