Two-Component Fullerene Molecular Layers Assembled on the Au(111) Substrate

Abstract

Self-assembly of binary and multicomponent colloidal crystals is an effective approach for the fabrication of structured new materials. The formation of colloidal crystals in most cases is controlled by optimized space occupation by the particles. C60 and C70 molecules, when treated as the smallest “colloidal particles”, can be used as model systems to study the formation of multicomponent molecular crystals in which the intermolecular forces are mainly of the van der Waals type. By deposition of C60 and C70 molecules onto Au(111), the mixing of the two molecules has been investigated. Both C60 and C70 form close-packed layers on Au(111), but with different lattice constants. At room temperature, the molecules within the molecular layer have complete freedom to rotate. The boundary between the C60 and the C70 domains consists of row dislocations. Adding C60 onto a C70 layer has an interesting effect in that C60 molecules can push their way into the C70 layer and force the C70 molecules to take a fixed upright configuration where the long axis of the molecule is perpendicular to the interface. Significant interlayer diffusion takes place at elevated temperatures. When C70 is added to a C60 layer, there is little evidence of C70 getting into the C60 layer. The second layer C70 forms a lattice-matched structure by taking the upright orientation.