Symmetry and Electronic Structure of Noble Metal Nanoparticles and the Role of Relativity

TL;DR

This study investigates the electronic structures of noble metal nanoparticles, revealing how symmetry and relativistic effects influence their electron states, with experimental spectra supported by density functional theory calculations.

Contribution

It demonstrates the impact of icosahedral symmetry and relativistic effects on the electronic structure of Cu, Ag, and Au nanoparticles, highlighting differences in degeneracy and structure.

Findings

Cu55- and Ag55- exhibit highly degenerate states due to icosahedral symmetry.

Gold clusters show low degeneracy, indicating lower symmetry structures.

Relativistic effects significantly influence gold's electronic structure.

Abstract

High resolution photoelectron spectra of cold mass selected Cu_n-, Ag_n- and Au_n- with n =53-58 have been measured at a photon energy of 6.42 eV. The observed electron density of states is not the expected simple electron shell structure, but seems to be strongly influenced by electron-lattice interactions. Only Cu55- and Ag55- exhibit highly degenerate states. This is a direct consequence of their icosahedral symmetry, as is confirmed by density functional theory calculations. Neighboring sizes exhibit perturbed electronic structures, as they are formed by removal or addition of atoms to the icosahedron and therefore have lower symmetries. Gold clusters in the same size range show completely different spectra with almost no degeneracy, which indicates that they have structures of much lower symmetry. This behaviour is related to strong relativistic bonding effects in gold, as demonstrated by ab initio calculations for Au55-.