Molecular dynamics investigations of surface damage produced by kiloelectronvolt self-bombardment of solids

Molecular dynamics computer simulations were employed to study damage production mechanisms at solid surfaces during bombardment with kilo-electronvolt ions. Three separate mechanisms are identified: ballistic damage, viscous How and microexplosions. Ballistic damage is created by the direct knock-on of atoms onto the surface as described within the binary collision approximation. Viscous flow refers to local melting and the forced flow of liquid onto the surface, and microexplosions occur when the high pressures in cascades lead to rupturing of the nearby surface. The relative importance of each mechanism depends on several parameters: atomic mass, melting temperature. atomic density, structure and atomic bonding of the target, and the mass and energy of the projectile. The simulations were performed for Pt, Au, Cu, Ni and Ge self-atom bombardment. Cascades in the interior of the targets were also examined to provide a comparison for the surface events. In addition several events of 4.5 keV Ne and Xe bombardment of Pt(lll) were simulated for comparison with experimental studies of these same bombardments using scanning tunnelling microscopy.