Chemical specificity in the surface diffusion of clusters: Ir on W(211)

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Abstract
Although the diffusion of tungsten and rhenium clusters over the (211) plane of tungsten has recently been found to be quite similar, a significant chemical specificity should be expected for cluster migration. Such specificity has now been established in quantitative measurements on iridium doublets diffusing on W(211). With tungsten and rhenium, dimers have a lower activation energy for diffusion than do single atoms. For iridium dimers, the situation is reversed: single atoms diffuse over a barrier of 51 ± 5 kJ mol−1, compared to a barrier of 65 ± 6 kJ mol−1 for dimers. This, and differences in the diffusion dynamics, are shown to be a consequence of interactions specific to iridium adatoms.

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