Van der Waals interactions mediating the cohesion of fullerenes on graphene

Fullerenes on single-layer epitaxial graphene are a model system to study very faint interactions at a molecular level. By a variable temperature scanning tunneling microscope we have been able to study ordered fullerene layers at 40 K, exclusively bound by van der Waals interactions. The experimentally determined adsorption geometry of the molecules is computationally confirmed only if van der Waals interactions are included in the calculation formalism. The relative orientation of fullerenes in their close-packed arrangement is found to be the crucial factor for determining the total energy. Observation of collective movements of fullerene islands points out the weak coupling to the substrate and the important role of the van der Waals cohesion forces withinP.M. acknowledges financial support from a Rafael Calvo Rodés scholarship. M.S. and P.J. acknowledge Grant No. GAAV IAA100100905 GACR, Project No. 204/10/0952. C.G. acknowledges the José Castillejo Grant from the Spanish Education Ministry and the CSIC JAE-DOC positio