Polycrystalline Cu, Cu₂₀Au₈₀, Cu₄₀Au₆₀, Cu₈₀Au₂₀ 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, CumAun₋m, containing n atoms, Yn, was found to follow a power in n, i.e. Yn∝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.
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms Vol. 267, Issue 16, p. 2757-2760