Surface Gliding of Large Low-Dimensional Clusters

Surface diffusion of a large cluster moving as a whole (“gliding”) is analyzed in the framework of a kinetic theory combined with an explicit treatment of intracluster motion. A “dynamical” misfit caused by the thermal vibrations of the cluster's atoms is shown to lead to a dramatic increase of the pre-exponential factor in the diffusion coefficient, while size effects in the cluster-substrate-bath coupling enhance the occurrence of long jumps for larger clusters. The results constitute an explanation of recent puzzling observations for compact 2D clusters ${\mathrm{Ir}}_{19}$ and ${\mathrm{Ir}}_7$ on the Ir(111) surface.