Ultraviolet photoabsorption spectra of silver and gold nanoclusters

Abstract

It has been previously proposed that the behaviour of visible optical absorption spectra of silver and gold nanoclusters can be explained by a two-region model in which dielectric screening by the core d electrons is ineffective near the cluster surface. In this paper we investigate the implications of this model for the ultraviolet (UV) region of the cluster photoabsorption spectrum. We find that there should exist additional distinct resonances at high (20–30eV) as well as near-UV (e.g., 4–6eV for Ag _n ) frequencies. The position of the near-UV peaks is shown to be a sensitive function of the cluster size and charge. This behaviour reflects an interplay between d-electron screening and valence-electron spill-out. The calculations show that measurements of the evolution of UV spectra of size-selected noble-metal clusters can provide stringent tests of the theory of surface structure and plasmon resonances of nanoparticles.