Molecular dynamics simulations of the initial stages of sputter erosion of a metal overlayer system: 2 keV Ar → Cu/Ni(1 0 0)

The initial sputter erosion of Cu/Ni(1 0 0) has been simulated using molecular dynamics. The morphological and compositional changes that accompany sputtering are described. Ar projectiles (2 keV) are delivered sequentially at 10 ps intervals into a 2000 Å2 region of the target, up to a nominal fluence of 1.1 × 1015 cm−2. Simulations were performed for several projectile–target geometries with normal, oblique and random altitudinal (ϕ) angles of incidence and 〈0 1 1〉, 〈0 0 1〉 and random azimuthal (ϕ) angles of incidence. As expected, the predicted rate of target erosion is lowest for normal projectile incidence, and increases for oblique bombardment geometries. The predicted sputtering properties show no significant dependence on ϕ (for ϕ = 70°). The principal effect of bombardment geometry is to alter the rate at which surface erosion proceeds. However, differences in the morphological development of the target are detected for the oblique bombardment geometry with ϕ = 30° (e.g. a reduction in the sputtered atom information depth). This geometry also causes a displacement (by 20 Å) of the sputtering crater from the centre of the primary impact zone. With reference to observations made on an experimental timescale, the simulations are deficient in terms of their ability to model diffusive processes, e.g. the annihilation of adatom monomers on terraces outside the primary impact zone.