Simulation of cluster ejection following high-energy Aun→Au(111) bombardment

Following the recent report by Andersen et al. of extremely large nonlinear sputtering yields caused by the bombardment of gold targets with small, high energy gold clusters [Phys. Rev. Lett. 80 (1998) 5433], we carried out simulations showing: (1) that the thermal spike phase of the collision cascade contributes significantly to these nonlinear yields; and (2) that individual ‘mega-events’ with yields up to ∼2500 contribute significantly to the total sputtering yields [Shapiro and Tombrello, Nucl. Instrum. Meth. B 152 (1999) 221]. Here we extend our simulations to examine the cluster component of the sputtering yield. We find that clusters with n≥2 constitute a large fraction of the yield. In the early stages of sputtering (≤3 ps) clusters with as many as ∼800 atoms are ejected. These very large clusters are not stable; however, after allowing the simulations to evolve for an additional 100 ps, clusters with as many as ∼300 atoms remain. The yields of clusters with n≤∼10 follow typical power law distributions, while the yield of clusters with n>∼10 significantly exceed the predictions of the power-law distribution. Our simulations also show that clusters with more than a few tens of atoms are emitted exclusively during the thermal spike phase.