C60 single crystal films on GaAs(001) surfaces

We report on a scanning tunnelling microscopy (STM) study, with different C₆₀ thin-film growth orientations, on As-rich 2×6 and 2×4 surfaces of GaAs(001) prepared by molecular beam epitaxy. On the 2×6 As surface, the corrugated potential of the 2×6 substrate forces the first monolayer to be strongly modified, resulting in the formation of a 'double-chain' commensurate structure. C₆₀-substrate interaction, however, is limited to 2 or 3 monolayers from the interface and a competing intermolecular interaction governs the 3-dimensional growth of multiple-layer C₆₀ FCC crystalline film. Even though both surfaces have similar strongly corrugated potentials, an unusual (110)-oriented C₆₀ thin crystalline film grows on the 2×4 β phase. This novel growth can be understood in terms of a site-specific interaction between the substrate and the molecule and the interplay of the competing intermolecular interactions.