Sputtering of clusters from copper–gold alloys

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-δYn∝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.