Effects of global versus non-overlapping thermal spikes on ion beam mixing efficiency in metals

Abstract

Abstract Ion mixing efficiency of metals, measured by employing marker experiments at low temperatures (<77 K), varies significantly in magnitude and exhibits different correlations with thermochemical and materials parameters. We have separated the available mixing data into two groups, for noble metals and for other transition metals, respectively, and compared them with phenomenological models formulated based on Vineyard's approach for thermally activated diffusive processes. Two different thermal spike configurations have been considered: well-developed global spikes, and thermal spikes in non-overlapping subcascades. The observed match between model-predicted trends and mixing data suggest that the observed variations in mixing data can be explained in terms of different characters of thermal spike development, i.e., global spikes in noble metals versus non-overlapping spikes in other transition metals. These results are compared with those for ion mixing in bilayers, where different thermal spike mixing behaviours have also been noted. In addition, our estimate of the activation energy for diffusion in thermal spikes is consistent with the notion of a liquid-like diffusion mechanism.