SURFACE EFFECTS ON DAMAGE PRODUCTION DURING ION-BOMBARDMENT - A MOLECULAR-DYNAMICS STUDY

Molecular dynamics investigations of self-ion bombardment of Au, Cu, Ge, and Pt were performed with ion energies in the range of 5-20 keV. These simulations revealed that the mechanisms of damage production near surfaces can be far different than those in the bulk. Local melting was observed to be a fundamental element in all of the simulations, In the metals, where the volume of melting is positive, pressure was created within the molten cascade core, and this led to the flow of atoms onto the surface. Upon solidification, relatively few atoms were able to return to lattice sites below the surface, leading to the formation of islands on the surface and dislocation loops of vacancy character, below. Similar effects of melting were obtained for Ge, but since the volume of melting is negative, a somewhat different damage mechanism arises. The simulations also provide new insight about the nature of nonlinear sputtering in metals with high atomic numbers.