Tunable Plasmonic Nanoparticles Based on Prolate Spheroids

Metallic nanoparticles can exhibit very large optical extinction in the visible spectrum due to localized surface plasmon resonance. Spherical plasmonic nanoparticles have been the subject of numerous studies in recent years due to the fact that the scattering response of spheres can be analytically evaluated using Mie theory. However a major disadvantage of metallic spherical nanoparticles is that their resonance wavelength is independent of the particle dimensions. In this paper, plasmonic resonance of spheroidal metallic nanoparticles is studied. Using the quasi-static approximation, the resonance condition for localized surface plasmon of spheroidal nanoparticles is derived. It is shown that unlike spherical nanoparticles in which the resonance wavelength is independent of the particle dimensions, the additional degree of freedom in spheroids allows for tuning the resonant wavelength. Additionally a formal approach to tune the surface plasmonic resonance of nano-spheroids to a wavelength of interest is presented. The results are confirmed by performing full-wave simulation for gold nanoparticles.