Defect-induced nucleation of sputter-deposited gold on graphite

The early stages of thin film formation are studied on atomic scale by scanning tunneling microscopy imaging. Gold is sputter deposited on a graphite substrate using Cs+ ion bombardment of a gold target at a few keV energy. Stable gold nuclei are formed at defect sites which are produced by the impact of gold atoms with energy larger than 180 eV. This energy is needed to displace a carbon atom from the lattice in a binary collision. Three-dimensional clusters grow by attachment of additional gold atoms to the nuclei. The fraction of gold atoms with energy larger than 180 eV depends on Cs+ ion energy and typically is less than one percent of the incident gold flux. After 1 s of deposition, the average size of the clusters is 10 atoms. Cluster density is 1012 clusters per cm2, and a few percent of the incident flux is condensed in the clusters. These phenomena are a consequence of the weak interaction strength between gold and graphite.