Sputterring and smoothing of metal surface with energetic gas cluster beams

Sputtering is a process of surface erosion by energetic ions. One of the remarkable effects of sputtering with cluster ions is surface smoothing. To understand its mechanism we have developed a computational model, which utilizes molecular dynamics (MD) to simulate rapid atomic collisions in the central impact zone, and a finite-difference method to account for processes occurring on a longer time scale over a wider target area. A case of gas cluster of a few hundred Ar atoms impacting a Cu target with energy up to 20 keV has been considered. The MD simulation has revealed that the atoms ejected from the surface have a significant lateral momentum component (parallel to the surface) which may have a major effect on surface morphology. Evolution of surface morphology under cluster ion irradiation was described by the modified Kuramoto-Sivashinsky equation. Comparison of the simulations with experimental data shows qualitative agreement.