It was recalled that recent computer simulations had shown that a nearby surface could lead to an appreciable increase in the numbers of vacancy defects which were produced by displacement cascades in pure metals. A study was made here of the effect of a surface upon the production of lattice defects by 10keV displacement cascades. This ordered alloy was chosen because previous simulations had shown that antisite defects, rather than Frenkel pairs, were the predominant defects that arose from cascades in the bulk. By choosing the primary recoil atom to be a surface atom, the effect of the surface upon the damage mechanisms was maximized. The production efficiency of vacancies was higher for near-surface events, whereas the corresponding efficiency for interstitials was greatly reduced. Most of the extra atoms were created as adatoms on the surface, because the number of sputtered atoms was insensitive to the cascade energy. As in the case of cascades in the bulk, the predominant defects were antisite atoms, and their production in a disordered zone was enhanced by between 25 and 50% by the surface. The surface produced a marked increase in vacancy clustering; to such an extent that vacancy dislocation loops could be produced in the disordered zone, due to cascade collapse at low cascade-energy levels.

Defect Production by Near-Surface Displacement Cascades in Ni3Al. Gao, F., Bacon, D.J.: Philosophical Magazine A, 1997, 75[6], 1603-23