Quantum well states in two-dimensional gold clusters on MgO thin films

TL;DR

This study investigates the electronic structure of ultra-small gold clusters on MgO thin films, revealing two-dimensional quantum well states and charge transfer effects, with implications for nanoscale electronic properties.

Contribution

The paper demonstrates the existence of 2D quantum well states in gold clusters on MgO and analyzes charge transfer and electronic structure using combined experimental and theoretical methods.

Findings

Gold clusters exhibit 2D quantum well states resembling a 2D electron gas.

Clusters gain 1-4 electrons from the interface due to charge transfer.

HOMO-LUMO gap closes for clusters with 70-100 atoms.

Abstract

The electronic structure of ultra-small Au clusters on thin MgO/Ag(001) films has been analyzed by scanning tunneling spectroscopy and density functional theory. The clusters exhibit two-dimensional (2D) quantum well states, whose shapes resemble the eigen-states of a 2D electron gas confined in a parabolic potential. From the symmetries of the HOMO and LUMO of a particular cluster, its electron filling and charge state is determined. In accordance to a DFT Bader-charge analysis, aggregates containing up to twenty atoms accumulate one to four extra electrons due to a charge transfer from the MgO/Ag interface. The HOMO - LUMO gap is found to close for clusters containing between 70 and 100 atoms.