Embedded-atom molecular dynamics simulations were used to monitor the dynamics of adatoms, vacancies and adatom/vacancy pairs on 2-dimensional hexagonal Pt19 clusters on Pt(111) surfaces at 1000K. All configurations were found to be quite stable and have essentially the same migration mobilities as compact hexagonal clusters. However, the presence of a single vacancy dramatically decreased the lifetime of an adatom on the cluster by a factor of three. This occurs primarily through an enhancement of the rate of push-out/exchange reactions at the outer cluster edge resulting from vacancy-induced softening of edge atom bonds. Overall, adatoms in the presence of vacancies descend to the terrace via vacancy filling 10% of the time, and through reactions with outer cluster edges the remaining 90%. Direct vacancy filling mechanisms were analogous to, and have similar activation energies with, those at outer cluster edges: adatom hopping over descending steps and push-out/exchange reactions.

Adatom/Vacancy Interactions and Interlayer Mass Transport in Small Two-Dimensional Pt Clusters on Pt(111). E.P.Münger, V.Chirita, L.Hultman, J.E.Greene: Surface Science, 2003, 539[1-3], L567-73

 Table 12

 Tracer Diffusivity of Fe in Pt3Fe