Study of Light Extinction and Surface Plasmon Resonances of Metal Nanocluster: a Comparison Between Coated and Non-coated Nanogeometry

Abstract

We suggest a noble design of coated and non-coated nanospheroids to study the tunable behaviour of surface plasmon resonances with different physical environments. Incorporation of coated nanospheroids into the various dielectric media exhibits double dipole plasmonic resonance spectra, which are highly tunable in the visible to infrared regions of the electromagnetic spectrum. The tunability of double dipole peaks and its spectral width depend upon the shape anisotropy of the chosen nanogeometry (especially prolate- and oblate-shaped coated silver and gold nanospheroids). By changing the major and minor axes radii of the inner ellipsoid, there is gradual blue and red shifting in the surface plasmon resonance (SPR) peak position. It was accounted that for the prolate-shaped coated gold nanospheroid with inner radii a ₁ = 10 nm and c ₁ = 3.8 nm and outer radii a ₂ = 16 nm and c ₂ = 6.08 nm, two SPR peaks are found at wavelengths 615 and 826 nm. In addition, the tunability of SPR peaks and full width at half maximum (FWHM) value have also been discussed with surrounding media and it was found that the magnitude of the peak extinction is maximum for refractive index N = 2. With the selection of various optical constants of embedding media, the wide tunability of plasmonic resonance spectra that lies in the range of 400–1100 nm has been observed. We have also discussed the advantage of coated nanospheroids over non-coated nanospheroids in the context of tunability of the SPR peak as well as the number of photons absorbed inside the thin-film wafer.