Molecular dynamics simulation of nonlinear effects in sputtering — Cu(100) targets

Abstract

Nonlinear effects in sputtering from Cu(100) targets have been simulated with the multiple-interaction molecular dynamics code SPUT2. Both dimer and single-ion impacts were studied for Ar, Cu, Kr, and Xe ions normally incident on Cu(100) with energies of 5 keV/atom. Statistically significant nonlinear yields were found for bombardment with Kr and Xe dimers, but not for Ar and Cu dimer bombardment. Even for those cases not exhibiting nonlinearities in yield, differences were found in the energy and angular distributions of sputtered atoms for dimer impacts compared to the sum of individual ion impacts. For both dimer and single-ion impacts most sputtering was found to occur within 200 fs of impact; however, atom ejection tended to be shifted to later times for dimer impacts. Likewise, energy degradation in the collision cascades was much slower for dimer impacts than for single-ion impacts. These results suggest that a thermal spike begins to develop relatively early in collision cascades initiated by dimer impacts on Cu. This developing spike together with collisional disruption of the surface contributes to the excess yield found with dimer impacts.