Liquid target generation techniques in molecular dynamics studies of sputtering

Abstract

Techniques of generating liquid targets for molecular dynamics studies of sputtering were investigated in systems consisting of 603 Cu atoms. The effects of different boundary conditions on sputtering yield, layer yield ratio, energy distribution, and polar angular distribution of ejected particles were found to be important. A box boundary condition and a semiperiodic boundary condition were considered. The box boundary conditions required the particles to experience pure reflection at the boundaries, while semiperodic boundary conditions demanded position and momentum periodicity in the two dimensions defined by the surface of the target. Sputtering from the target generated with a box boundary condition resulted in a 60% higher total yield, a slightly higher first layer yield ratio, a 60% lower surface binding energy, and a sharper polar angular distribution than from the target generated under a semiperodic boundary condition at the same temperature. Since the results obtained with the semiperiodic boundary conditions are in better agreement with experimental sputtering results, we have concluded that the semiperiodic boundary conditions produces a target that better represents the free surface of real liquid systems.