  Scanning tunneling microscopy combined with molecular dynamics simulations
reveal a dislocation-mediated island diffusion mechanism for Cu on Ag(111), a
highly mismatched system. Cluster motion is tracked with atomic precision at
multiple temperatures and diffusion barriers and prefactors are determined from
direct measurements of hop rates. The non-monotonic size dependence of the
diffusion barrier is in good agreement with simulations and can lead to
enhanced mass transport upon coarsening, in surprising contrast to the
traditional island diffusion models where diffusivity reduces with cluster
size.
