Experiment and simulation of cluster emission from 5 keV Ar→Cu

The abundance distribution of neutral Cu, clusters sputtered by 5 keV Ar impact from a polycrystalline Cu surface is measured using single-photon laser post-ionization. Molecular dynamics computer simulation is used to gain insight into the cluster sputtering process. Three different codes and two potentials are used to check the sensitivity of the results on numerics and physical input. Differences in the results obtained by the various codes and the different potentials used are discussed. While the total sputter yield is consistent with experiment, the fraction of atoms bound in clusters, and in particular the dimer fraction, are overestimated by at least a factor of 4. This is also true for a many-body potential which has been fitted to describe both bulk Cu and dimers. In detail, the simulation shows that larger clusters are emitted at later times from the target. Clusters originate mainly from regions of the surface, which are around the melting temperature of bulk Cu. Large clusters are emitted preferably from ion impacts with a high individual sputter yield. Finally, we simulate sputtering from a model Cu material with an artificially decreased cohesive energy. Here, drastic high-yield events (up to Y = 78) can be observed, which produce clusters abundantly. (C) 1998 Elsevier Science B.V. All rights reserved.