A molecular dynamics study of Cu dimer sputtering mechanisms

Molecular dynamics simulations were used to investigate the mechanisms responsible for the sputtering of dimers from Cu(100) and Cu(111) surfaces following bombardment by normally incident, 5 keV Ar^+ ions. Simulations were carried out using both a pair-potential and a many-body, embedded-atom potential to describe the Cu-Cu interaction. Computer animation techniques which allowed visual inspection of individual dimer trajectories were used to identify the mechanisms responsible for dimer ejection. In the pair-potential simulations dimers accounted for about 5% of the sputtering yield from both the (100) and (111) surfaces, while in the embedded-atom simulations dimers accounted for approximately 2% of the yield from the (100) and (111) surfaces. Three mechanisms were found to be responsible for the bulk of the dimer ejection events. Direct ejection of intact dimers and recombination in or near the surface were the most prevalent mechanisms observed. Less frequent, but still significant numbers of "push-stick" events were also seen. The simulations suggest that the sputtering of dimers is the result of competing mechanisms that take place preferentially towards the later phase of collision cascades that produce relatively large numbers of sputtered atoms.