Molecular dynamics simulations of inelastic energy loss effects in sputtering

Previous molecular dynamics (MD) simulations of inelastic energy loss effects in sputtering, which have employed pair potentials and velocity dependent losses [1,2], have attributed significant reductions in sputter yield (up to 40%) to energy losses in atom-atom collisions. Similar simulations, in which the average electron density is replaced by the local electron density as calculated from the embedded atom method (EAM) and Thomas-Fermi local densities, also yield significant inelastic energy losses in the collision cascade [3]. We present a preliminary account of EAM MD inelastic energy loss simulations using both a velocity dependent model to account for losses from collisions with valence electrons only, and an instantaneous loss model to account for collisions with core electrons. With this model we find that losses attributable to collisions with valence electrons and atom-atom collisions involving core electrons produce negligible reductions in sputtering yield. If ion-atom collisions involving core electrons also are included, sputtering yield reductions comparable to the continuous loss model are observed. However, in contrast to the continous loss model, angular distributions of sputtered atoms from the Cu(100) surface are affected by the inelastic losses. (orig.)