Deposition and diffusion of size-selected (Ag400+) clusters on a stepped graphite surface

We have investigated the deposition (at 500 eV) and subsequent diffusion of Ag-400 clusters on a stepped graphite surface by a combination of scanning electron microscopy experiments and computer simulations (molecular dynamics and Monte Carlo methods). We find that the shape of the clusters is only partially deformed by the impact with the surface, moreover the clusters do not create surface defects upon landing, and so are able to diffuse freely over the surface. Many clusters are found to become trapped at surface steps, where their mobility is reduced by the higher binding energy. Exploring the 1-D diffusion of clusters along the steps reveals the low mobility for larger islands, as well as the importance of defects on the step (for example kinks), which trap the mobile clusters.