Thermal Diffusion of C60 Molecules and Clusters on Au(111)

Abstract

The structure and dynamics of partial monolayers of C60 on the Au(111) surface were observed by scanning tunneling microscopy (STM) under ambient conditions. At submonolayer coverages, C60 molecules group into islands, and while the molecules in the interior of islands are quite stable, the C60s at island edges are less so, and their motions can be observed in real time using STM. The motion of surface-adsorbed C60 is predominantly the result of thermal diffusion; the extent of perturbation by the STM tip is determined to be minimal, using a quantitative analysis of a time series of STM images. Further analysis shows that motion of single C60 molecules is relatively uncommon, and that most diffusion of C60 on the surface occurs through the correlated or cooperative motion of molecular clusters ranging in size from 2 to 8 C60 molecules. Cluster diffusion is explained by a proposed “anchoring” mechanism, in which the stability of each C60 varies according to its position and orientation relative to the surface and to neighboring molecules.