Sputtering of clusters from copper–gold alloys

Abstract

Polycrystalline Cu, Cu 20Au 80, Cu 40Au 60, Cu 80Au 20 and Au samples were bombarded with 15 keV Ar +, and the resulting secondary neutral yield distribution was studied by non-resonant laser post-ionisation mass spectrometry. Neutral clusters containing up to 15 atoms were observed for the targets. The yield of neutral clusters, Cu m Au n − m , containing n atoms, Y n , was found to follow a power in n, i.e. Y n ∝ n - δ , where the exponent δ varied from 5.2 to 10.1. For a fixed n, the cluster yields showed a variation with number of copper atoms, m, much greater than expected for a binomial distribution suggesting that the clusters are not formed randomly above the surface and a component of preformed cluster emission occurs. In addition, the cluster compositions from the sputtered alloys were indicative of sputtering from a copper rich surface.