Vibrational modes of metal nanoshells and bimetallic core-shell nanoparticles

TL;DR

This paper provides a theoretical analysis of vibrational modes in metal nanoshells and bimetallic core-shell nanoparticles, revealing how their frequencies and damping rates depend on structure and environment.

Contribution

It offers the first detailed calculation of vibrational spectra for these nanostructures, including effects of environment and shell thickness.

Findings

Breathing mode frequency is lower in nanoshells than in solid particles.

Damping rates increase as shell thickness decreases.

Higher mode frequencies are environment-independent, damping is environment-sensitive.

Abstract

We study theoretically spectrum of radial vibrational modes in composite metal nanostructures such as bimetallic core-shell particles and metal nanoshells with dielectric core in an environment. We calculate frequencies and damping rates of fundamental (breathing) modes for these nanostructures along with those of two higher-order modes. For metal nanoshells, we find that the breathing mode frequency is always lower than the one for solid particles of the same size, while the damping is higher and increases with reduction of the shell thickness. We identify two regimes that can be characterized as weakly damped and overdamped vibrations in the presence of external medium. For bimetalllic particles, we find periodic dependence of frequency and damping rate on the shell thickness with period determined by mode number. For both types of nanostructures, the frequency of higher modes is nearly independent of the environment, while the damping rate shows strong sensitivity to outside medium.