We have explored the deposition of size-selected Ag-N(+) clusters (N=50-200) onto the graphite surface (at room temperature) over the impact energy range of 250-2500 eV, via a combination of scanning tunneling microscopy experiments and molecular dynamics simulations. We show that the clusters are pinned to the surface when the impact energy exceeds a critical value, which is proportional to the cluster size, N, via the formation of a point defect at the impact site. This prevents lateral diffusion of the clusters even at room temperature.