Molecular dynamics simulations of sequential cluster ion impacts

Molecular dynamics (MD) simulations of cluster and solid target collisions were performed in order to understand the relationship between surface deformation processes and cluster sizes. MD simulations of single impacts of clusters with various sizes showed that, when a cluster size is less than 10 000 atoms, a crater-like damage could be caused at 20 keV of total energy, while no damage was observed at Ar10 000 and Ar20 000 clusters. The surface morphology change was examined by MD of sequential irradiation of Ar clusters under various conditions. When the initial roughness of the surface was about 10 Å in r.m.s. and the total incident energy was 20 keV, the surface roughness was reduced with the impact of Ar13 333 or larger cluster. The MD results give information about the final value and decay speed of surface roughness, which are required to optimize the cluster ion irradiation condition for various nano-scale modification processes.