Cluster size dependence of the impact process on a carbon substrate

Molecular dynamics simulations of various sizes of carbon molecule as clust ers impacting a carbon substrate are performed in order to examine the size -dependence of the cluster ion on the impact process. Highly Oriented Pyrol itic Graphite (HOPG) was irradiated with C-1, C-4, C-8, C-19 and C-60 clust ers carrying the same energy-per-atom of 2 keV/ atom. When the cluster size is less than eight, interspersed damage is formed by the cascade-collision mechanism, whereas C-19 and C-60 impacts show homogeneously damaged region s in the surface of the substrate. In the case of large cluster ion impacts , all the incident energy of a cluster is deposited with high density in na rrow region on the surface. These results show good agreement with experime ntal STM observations of single traces induced by the impact of C-60 and sm all carbon molecules. (C) 1999 Elsevier Science B.V. All rights reserved.