Interfacial and intermolecular interactions determining the rotational orientation of C60 adsorbed on Au(111)

•Molecular orbital imaging of C60 on Au(111)-substrates by UHV-STM•The (2√3 × 2√3)R30°-structure consisting of dim and bright C60 is given in detail.•The rotational orientation of bright C60 is influenced by the next neighbors.•Two kinds of molecular orbital appearance of dim C60 are identified.•The alignment of dim C60 in one domain is determined by Coulomb interactions.

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√3 × 2√3)R30°-superstructure of C60 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 C60-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 C60-molecules in hex-vac positions are identified which are caused by the respective interaction with the facets surrounding the Au-vacancy.

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