A new approach to sputtering simulations from rare gas solids

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Abstract
Classical molecular dynamics simulations of sputtering using large samples of up to 15 500 particles are demonstrated for Lennard-Jones solids. Two features are introduced to represent the effect of the surrounding solid substrate. First, the outermost particles on each side of the sample are subjected to an additional harmonic potential restraining them close to the equilibrium position. Second, these outermost particles are maintained at a preset temperature by assigning velocities at each time step randomly from the corresponding Gaussian distribution. This boundary thermostat produces a ‘‘sandbag’’ effect and provides a means for excess kinetic energy to dissipate out of the sample. Preliminary results were obtained for single trajectories at 45° incidence and these illustrate that the sputtering yield from these model rare gas solids is strongly dependent on both the length of the simulation and the size of the sample. Simulations were continued to times in excess of 25 ps after which time for the largest sample there was some recoalescence of particles remaining in the surface region of the substrate. The long time sputtering yield was about 500 atoms which is comparable with experimental data on rare gas solids. It is demonstrated that particles within a cluster are just as likely to arise from nonadjacent sites as from near neighbors in the original lattice.