Numerical Study of Surface Plasmon Resonance of Bimetallic Au-Ag Core-Shell NanorodsDownload PDF
Some metal nanoparticles show distinctive surface plasmon resonance (SPR) bands that consist of intense photo-absorption and light scattering. Because of this characteristic, these nanoparticles are suitable probe materials for sensing and imaging of bio-related materials or for selective targeting in photothermal thearapeutics. The SPR bands come from the collective oscillation of free electrons in nanoparticles that are in resonance with the electromagnetic waves. The resonance frequency strongly depends on the shape and morphology of the nanoparticles. Anisotropic metal nanoparticles have been attractive research targets, because they showed multiple SPR bands in the visible and near infrared regions. Gold and silver core/shell nanorods were known to be uniform rod-shaped metallic core coated with another metallic shell, which clearly showed several surface plasmon bands that originated from the transverse and longitudinal SPR oscillations. In this work a model based on the finite element method (FEM) is developed to investigate the optical properties of Au-core/Ag-shell and Ag-core/Au-shell nanorods with different shell thickness and core aspect ratio. The numerical results that we have obtained show that the absorption spectrum of Au-core/Ag-shell nanorods present three resonance peaks respectively in: near-infrared, visible and ultraviolet regions. Whereas for the Ag-core/Au-shell nanorods the absorption spectrum present two resonance peaks, in near-infrared and ultraviolet regions. For the two cases, the position and amplitude of the various resonance peaks are strongly depends on the molar fraction of composition and core aspect ratio.
Keywords: Gold-silver core-shell nanorods, optical properties, surface plasmon resonance, finite element method.