Molecular dynamics study of surface erosion and defect generation in copper under cluster bombardment: influence of projectile mass and energy

Abstract

Using classical Molecular Dynamics (MD) method we study surface erosion, primary defect production and sputtering processes occurring in crystalline Cu target with (111) surface plane under irradiation with Cu N and Au N monomers and polyatomic clusters (N = 1-55) with incident energies E/N = (100-1000) eV per one incident atom. Non additive effects in both sputtering and defect production were observed in case of cluster impact above a certain threshold cluster size (N th ) which depends on both incident energy and mass of the projectile. The relative efficiency of sputtering (rescaled per one incident atom) is found to be about of factor of two larger then corresponding efficiency of damage production. It was demonstrated that most typical kinds of damage produced inside the target after projectile impact are vacancies and vacancy clusters, and their number significantly prevails over number of interstitials. Moreover, the fraction of interstitial atoms reduces strongly with increase of cluster size N at a given energy per one incident atom. This fact can be explained taking into consideration high mobility of interstitial atoms, which result in formation of ad-atom conglomerates on the surface. Impact of a cluser with N ≥ 6 and with total incident energy above some threshold value (about 5 keV) results in formation of pronounced microcrater surrounded by ad-atom rim, whereas below this energy threshold, typical topographic features of the impact region is either ad-atoms hillocks or shallow crater.