KEV-ATOM BOMBARDMENT OF CONDENSED RARE-GASES - MOLECULAR-DYNAMICS SIMULATION

We study by molecular dynamics simulation the phenomena occurring in a condensed amorphous Ar target induced by bombardment with a 1 keV Ar atom. We monitor the evolution of atom density and velocity in the target, the propagation of a shock wave in the initial phase, the distribution of kinetic and potential energy in the bombarded volume, and the energy spectrum of sputtered particles. We show that, among the 100 events studied, the most probable outcome is the formation of a huge cavity in the target of some 50 angstrom diameter. In this case, the sputter yield Y is very small, Y < 30. If this cavity is situated close to the surface, the surface disrupts and hundreds of atoms are emitted into the vacuum above the target. The emission is driven by the high energy density and pressure building up in the core of the atom-induced collision cascade. Thermalization of the collision cascade and equilibration with its surroundings requires around 20 ps. Finally, we comment on the relationship of our results to existing models of condensed gas sputtering, and on the fluence dependence of sputter yields.