The nature and annealing characteristics of ion radiation damage in gold, silver and copper

Abstract

Abstract Thin films of gold, silver and copper epitaxially grown with orientation {100} onto NaCl substrates have been irradiated with Ar ions with energies up to 5 kev, the total doses being in the range of 1015-1017 ions cm−2. The resulting damage structure, as well as its recovery behaviour in the course of thermal treatments, have been investigated by transmission electron microscopy. The damage is localized in a surface layer ≃ 70 Å thick and two main components may be distinguished : one consisting of small unresolvable defects, the other consisting of clearly resolvable dislocation loops either round or elongated. Dynamical diffraction contrast analysis shows that the loops have Burgers vectors α/2〈110〉 parallel to the surface and are interstitial in character. The Burgers vector direction is obtained by direct comparison with the stacking-fault traces and no complicated manipulations are required. On the other hand, in the light of their annealing behaviour, it is proposed that the unresolvable defects are small three-dimensional interstitial clusters. The annealing process involves three stages. In stage A, the small clusters anneal out by emitting interstitials, a fraction of which make loops grow. In stage B, the round loops anneal out by capturing vacancies with an activation energy slightly lower than that of self-diffusion for the corresponding metal. At the same time, constrictions appear on the elongated loops, that finally split into round loops. Self-climb is thought to be the mechanism responsible for this behaviour. Finally, in stage C the loops originated by the former mechanism anneal out by self-diffusion.