Plasmons of hollow nanobar oligomers

Abstract

Assembling metal nano-objects into well-defined configurations is an effective way to create hybrid plasmonic structures with unusual functionalities. Here we present a quantum mechanical investigation of the plasmon coupling behaviour of hollow nanobar oligomers. Specifically, we considered plasmonic oligomers made of an octamer (eight-member ring) and a nonamer (nine-member ring: an octamer with an additional hollow nanobar in the center) composed of magnesium atoms. We base our calculations on time-dependent density functional theory. The optical absorption spectra show interesting developments as a function of the ring radius, matching well with the available experimental results. We demonstrate that the presence of an additional hollow nanobar in the ring center produces a bimodal absorption peak in the optical spectrum, resembling a Fano resonance. Additionally, both the octamer and the nonamer exhibit a large spectral reduction for d = 7 Å, due to the onset of electron tunnelling. Our theoretical results may help the design of plasmonic oligomers using Earth-abundant metals.