Possible mechanisms for the formation of bumps, of atomic dimensions, in surface layers under low-energy single-ion bombardment were investigated. The results of molecular dynamics simulations were compared with experimental data which had been obtained by means of scanning tunnelling microscopy. Only the early stages of bump formation were considered. The depth profile of the momentum which was deposited into the cascade was evaluated and was used, together with the atomic density profile, to characterize inter-layer distortions. The surface bumps appeared under the influence of stresses which developed in the near-surface layers; due to defects that were created by the collision cascades. Such bumps originated at the positions of vacancies and interstitials, and were stabilized by the presence of inter-layer interstitials.

A.Gras-Marti, R.Smith, K.Beardmore, J.J.Jimenez-Rodriguez, V.Konoplev, J.Ferron: Computational Materials Science, 1995, 3[4], 413-22