Structure and dynamics of fullerenes adsorbed on the Au(111) surface

Scanning tunneling microscopy was used to characterize the structure of partial monolayers of C-60 and C-70 on the Au(111) surface. Both 2root3 x 2root3 R3degrees and 7 x 7 lattice symmetries were observed for C-60 monolayers, in accordance with previous results. For C-70 monolayers, structures are observed with rotation angles of 0degrees, 30degrees, and 14degrees with respect to the underlying substrate; we propose a previously unreported root13 x root13 R13.9degrees lattice structure to explain this last observation. Time sequences of STM images show that while fullerene monolayers are largely stable, molecular motion can be observed on the timescale of minutes or hours. For C-60, thermal diffusion is the predominant cause of this motion, and STM perturbation of the sample is negligible. In contrast, C-70 is observed to diffuse far more slowly; under normal scanning conditions, tip-induced motion is the major effect.