Low energy alkali ion scattering investigation of Au nanoclusters grown on silicon oxide surfaces

Abstract

The atomic and electronic structures of Au nanostructures grown by deposition onto various silicon oxide surfaces were probed with low energy alkali ion scattering. Charge state-resolved time-of-flight spectra of scattered 2 keV 39K + ions were collected from Au deposited onto an untreated Si wafer with a native oxide, a thermally grown oxide surface, and atomically-clean Si(111). It is shown that nanoclusters form on both oxides, but not on the clean Si. A quantitative analysis of the ion scattering spectra indicates that the nanoclusters are initially flat, two-dimensional structures that start to develop a second layer at about 0.5 Å of deposited Au and then form three-dimensional islands. The neutral fraction of scattered 2 keV 39K + ions decreases with deposition indicating changes in the quantum state occupancy with cluster size. The shapes of the clusters differ on the native and thermal oxides, leading to shape-dependent neutralization.