Research On Extinction Properties Of Compound Nanoparticles Based On Discrete Dipole Approximation

Localized Surface Plasmon Resonance（LSPR） is a special kind of properties that formed by the interference between metal surface electron and incident light. LSPR is strongly dependent on the shape, size, material and refractive index of the surrounding medium of noble metal nanoparticles, which can be delicately engineered to meet different requirements. Recently, some composite nanostructure composed of compound and silver and gold nanoparticles could create abundant tunable LSPR modes in several regions, especially in the infrared region, which have potential applications in SERS, biosensing and photocatalysis. In this paper, the influence of material, size and refractive index of the surrounding medium on the surface plasmon resonant characteristic of multilayered nanoshells and spherical wedges nanoparticles are investigated by the discrete dipole approximation based on the plasmon hybridization theory.The numerical results indicate that the extinction spectrum of two layer nanoshell is red shifted with the increase of metal nanoparticle core-shell ratio and the refractive index of the surrounding medium. The electron transfer is existed between the compound nano-core and the silver nanoshell, and the level of reduced surface electronic density of silver nanoshell with the same size from the highest to lowest is Cd S/Ag, Zn S/Ag, ITO/Ag. Additionally, the level of extinction properties of gold nanoshell with the same size from the highest to the lowest is ITO/Au, Nb-Sn/Au, Cd S/Au.It is found that the resonance wavelengths of Au/interlayer/Ag, Ag/ITO/Cd S/SiO₂ multilayered nanoshells and Ag/ITO sphere wedges nanoparticles show a remarkable dependence on the shell thickness, gap distance, different kinds of interlayer materials and refractive index of the surrounding medium. The resonance peak of Au-Cu-Ag is blue-shifted with the increase of gold core ratio and only one resonance peak exist in the extinction spectrum, whereas the peak of Au-ITO-Ag is red-shifted with the increase of gold core ratio and refractive index of the surrounding medium and three energy modes（?） 、（?）and（?）exist in the spectrum. In the contours of the electric field enhancement of the Ag/ITO spherical wedges, electric field is mainly distributed in the gap region of sliced nanosphere and the central point.