Scanning tunneling microscopy of surface-adsorbed fullerenes: C60, C70, and C84

Scanning tunneling microscopy (STM) is used to characterize partial monolayers of C60, C70, and C84 adsorbed on the Au(1 1 1) surface at room temperature and under ambient conditions. A high degree of structural polymorphism is observed for monolayers of each of these fullerenes. For C60, three lattice packings are observed, including a previously unreported 7 × 7 R21.8° structure that is stabilized by adjacent surface step defects. For C70, two lattice packings are observed, and analysis of molecular features in STM images allows molecular binding geometry to be determined. In one of the two observed lattice structures, C70 molecules align their long axis along the surface normal, while in the other, molecules align parallel to the surface and along a gold lattice direction. The parallel geometry is also preferred for isolated and loosely packed molecules on the surface. C84 exhibits a large number of lattice orientations and no long-range order, and likely binds incommensurately on Au(1 1 1). Time series of images of partial C70 monolayers show progressive surface modification as a result of perturbation by the STM tip; this is in contrast to the behavior of C60, where alterations in surface structure at room temperature are thermally driven.