Molecular dynamics simulations of inelastic energy loss effects in sputtering II
Previous molecular dynamics (MD) simulations of inelastic energy loss effects in sputtering, which have employed pair potentials and velocity-dependent losses, have attributed significant reductions in sputtering 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 electron densities also yield significant inelastic energy losses in the collision cascade [A. Caro and M. Victoria, Phys. Rev. A 40 (1989) 2287]. Here we report results of EAM MD inelastic energy loss simulations for the Ar^+-Cu system for bombarding energies from 1 keV to 5 keV using a model that includes velocity-dependent losses for collisions with valence electrons and instantaneous losses for collisions involving 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. The inclusion of instantaneous losses from ion-atom collisions, however, produces significant reductions in sputtering yield above a bombarding energy threshold of approximately 2 keV. The polar-angle distributions of atoms sputtered from the Cu(100) surface also are changed significantly by this inelastic loss model.
© 1994 Elsevier Science B.V. Received 24 January 1994; revised form received 8 July 1994. Supported in part by the National Science Foundation [Grants DMR90-02532 and DMR93-12468 at CSUF and Grant DMR93-18931 at Caltech).