Sputtering of clusters from metal surfaces

When an energetic ion strikes a surface, both atoms and clusters of atoms may be desorbed. Surface analysis techniques such as SIMS (secondary ion mass spectrometry) or SNMS (secondary neutral mass spectrometry) typically use the atomic signal to derive information on the surface composition. However, clusters carry extra information about the surface, since they preferentially come from the top surface layer, in contrast to atoms which may also be desorbed from the second layer of atoms in a surface. Clusters are also preferentially formed from neighbouring atoms and so can give information on surface segregation. Such work prompts the questions like the following related to formation mechanisms of cluster sputtering: Do more strongly bound species preferentially form mixed clusters? What is the relative importance of cluster formation and cluster fragmentation processes in producing stable clusters? How does the composition of the clusters compare to the composition of the original surface? In this paper we show results for Aln, Nin and mixed NinAlm neutral clusters sputtered from surfaces by Ar ion beams. 11 refs., 5 figs. 001NZ0700013