Nucleation and growth of C60 thin films on graphite

We present a scanning tunnelling microscopy study of C60 thin films evaporated onto the basal plane of highly orientated pyrolytic graphite under ultrahigh vacuum conditions. For deposition at room temperature and with low deposition rates, it was found that C60 islands nucleate and grow directly from steps on the surface. The height of the step has a direct influence upon the size of the island. These primary islands were observed to grow through the formation of stable bilayer islands, which extended parallel to the substrate to produce large flat islands with local heights of up to 4 ML (indicating some three-dimensional growth). By contrast, for deposition on to substrates heated to 100°C, layer-by-layer growth was found to dominate. This suggests that the three-dimensional growth observed at room temperature is kinetically limited.