A molecular dynamics simulation study of the influence of the ion mass upon atom ejection processes

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Abstract
A molecular dynamics simulation has been used to investigate the ion mass dependence of single-crystal atom ejection. Atom yield ratios, surface damage cross sections, atoms ejected per single ion (ASI) distributions, ejected atom energy distributions, layer yield ratios, and multimer yield ratios have been computed for normally incident Ne, Ar, Cu, Kr, and Xe ion masses on Cu targets for two very different Born-Mayer ion-atom potential functions. Results are compared with experimental data where feasible. The sputtering yield is found to increase with the ion size, as fixed by the ion-atom potential function, not with the ion mass. Experimental ejected atom energy distribution functions should show an ion mass dependence at higher atom energies. The layer yield ratios decrease as the ion mass increases. The heavier ions show no increased tendency to eject clumps of material or to create large, deep craters in the target surface. Atoms driven into the target may make a significant contribution to near-surface depleted zones and crater formation. The multimer yield ratios show very little ion mass dependence. ASI distributions and surface layer damage distributions show how momentum changes at constant ion energy affect the sputtering dynamics.