Stopping of energetic cobalt clusters and formation of radiation damage in graphite

The interaction of energetic (up to 200 eV/atom) size-selected Con clusters with HOPG is studied both experimentally and theoretically. Etching of the radiation damaged areas introduced by cluster impacts provides a measure of the depth to which the collision cascades are developed and allows a comparison of these data with the molecular dynamics simulations. Good agreement between the experimental results and modeling is obtained. It is shown that the projected range of the cluster constituents can be linearly scaled with the projected momentum (the cluster momentum divided by surface impact area). With decrease in cluster energies to ca. 10 eV/atom the transition from implantation to pinning is suggested. It is found that even after quite energetic impacts residual clusters remain intact in the shallow graphite layer. These clusters can catalyze reaction of atmospheric oxygen with damaged graphite areas under the thermal heating that leads to the formation of narrow (5-15 nm) random in shape surface channels (trenches) in the top few graphene layers. Thus, small imbedded Co nanoparticles can be used as a processing tool for graphene.