Electronic Structure and Bonding of Icosahedral Core-Shell Gold-Silver Nanoalloy Clusters Au_(144-x)Ag_x(SR)_60

TL;DR

This study uses density functional theory to analyze the electronic structure and bonding in icosahedral gold-silver nanoalloy clusters, revealing how silver incorporation influences electronic properties and optical absorption.

Contribution

It provides a detailed theoretical model of Au-Ag nanoalloy clusters, highlighting the effects of silver on electronic shell structure and optical transitions, which was not previously characterized.

Findings

Silver enhances electron shell structure near the Fermi level.

Absorption spectrum shows structured features around 0.8 eV.

Element-dependent interband transition edges are predicted.

Abstract

Atomically precise thiolate-stabilized gold nanoclusters are currently of interest for many cross-disciplinary applications in chemistry, physics and molecular biology. Very recently, synthesis and electronic properties of "nanoalloy" clusters Au_(144-x)Ag_x(SR)_60 were reported. Here, density functional theory is used for electronic structure and bonding in Au_(144-x)Ag_x(SR)_60 based on a structural model of the icosahedral Au_144(SR)_60 that features a 114-atom metal core with 60 symmetry-equivalent surface sites, and a protecting layer of 30 RSAuSR units. In the optimal configuration the 60 surface sites of the core are occupied by silver in Au_84Ag_60(SR)_60. Silver enhances the electron shell structure around the Fermi level in the metal core, which predicts a structured absorption spectrum around the onset (about 0.8 eV) of electronic metal-to-metal transitions. The calculations also imply element-dependent absorption edges for Au(5d) \rightarrow Au(6sp) and Ag(4d) \rightarrow Ag(5sp) interband transitions in the "plasmonic" region, with their relative intensities controlled by the Ag/Au mixing ratio.