The impact of size-selected ag clusters on graphite: An STM study

We have used the scanning tunnelling microscope (STM) to investigate the deposition of size-selected (Ag-n)(+) clusters, in the size range 50-400 atoms, on highly oriented pyrolytic graphite (HOPG). The cluster morphology has been explored as a function of impact energy. For high deposition energies (similar to 10 ev/atom) the clusters are pinned to the surface and flattened on impact. For lower impact energies (similar to 1 eV/atom) the footprint of the cluster on the surface is significantly reduced. By controlling the deposition parameters clusters have also been selectively sited at surface steps. Larger particles, arising from diffusion and aggegation of deposited clusters, are visible with the scanning electron microscope (SEM) but not the STM; we find definite evidence that the interaction with the STM tip disturbs these particles.