DIFFUSION AND AGGREGATION OF LARGE ANTIMONY AND GOLD CLUSTERS DEPOSITED ON GRAPHITE

We present a study of the first stages of growth of thin films produce d by low-energy cluster beam deposition (LECBD) on graphite. Our exper iments are analyzed in the framework of new models including three phy sical ingredients, which are the deposition, the diffusion and the agg regation of the clusters. The comparison between computer simulations of the model and the experimental structures reveals that only the inc ident clusters diffuse on the graphite, the dusters stick irreversibly upon contact, and allow us to quantify the diffusion of clusters on g raphite. Two kinds of metallic cluster films are studied: thin films p roduced by deposition of antimony clusters (containing 2300 and 250 at oms) and others by deposition of gold clusters (containing about 250 a toms). In both cases, we find that the clusters, in spite of their lar ge size, diffuse very rapidly on the surface. The different microscopi c diffusion mechanisms proposed in the literature are investigated, bu t none is compatible with our experimental results. Finally, we sugges t a collective mechanism where the cluster rotates on the surface as a rigid entity to explain our results.