Study of Surface Plasmon Resonances of Core-Shell Nanosphere: A Comparison between Numerical and Analytical Approach

Abstract

An investigation of the wavelength dependent extinction spectra of coated sphere with different core@shell compositions based on discrete dipole approximation technique has been presented in this paper. We have used combinations of A g, A u, and S i O 2 for this analysis. Specifically, we study the impact of spherical core-shell thickness on its surface plasmon resonance (SPR) peak positions and corresponding spectral widening in distinct regimes of the spectrum. We observe that SPR peak of core-shell nanoparticle(CSNP) can be tuned over the visible to near-infrared spectrum region by manipulating the core/shell ratio and composition of core and shell. Specifically, for dielectric@metal (core@shell) nanoparticle, SPR peak position shifted towards lower wavelength as we increase the shell thickness, which is opposite to the SPR behavior of metal@dielectric. The extinction spectrum shows linear relation between SPR position and thickness of the shell. Further, we observed two resonant peaks for the case of metal@metal CSNP. The SPR peak of Au@Ag (a eff 100 nm with shell thickness 8 nm) reveals two resonant peak corresponding to Au (594 nm) in red domain, while the peak in blue domain corresponds to Ag (402 nm). We also observe that optical resonance of CSNP can be tuned across the near-infrared region by changing the surrounding medium of higher refractive index. Further, near field pattern of core@shell geometry at resonance wavelength is also shown in the present study. We have also compared the numerical and analyticalmethod for smaller size CSNP with varying thickness and the results show good agreement.