Interfacial and intermolecular interactions determining the rotational orientation of C sub(60) adsorbed on Au(111)

Close-packed monolayers of fullerenes on metallic substrates are very rich systems with respect to their rotational degrees of freedom and possible interactions with different adsorption sites or next neighbours. In this connection, we report in detail on the (2[radic]3 2[radic]3)R30 degree -superstructure of C sub(60) with respect to the Au(111)-surface. We use molecular orbital imaging in systematic UHV-STM studies to reveal the delicate balance of interfacial and intermolecular interactions in this system. Thus, bright C sub(60)-molecules in 5:6-top and 6:6-top geometries are observed depending on the respective next neighbours. Moreover, tiny changes in the appearance of the unoccupied molecular orbitals of dim C sub(60)-molecules in hex-vac positions are identified which are caused by the respective interaction with the facets surrounding the Au-vacancy.