High-resolution studies of C 60 films by scanning tunnelling microscopy

Abstract

Scanning tunnelling microscopic studies of C 60 films containing conducting islands, under ambient conditions, have revealed the characteristic FCC lattice of the C 60 clusters with intermolecular distances in various planes along different crystallographic directions closely matching with the diffraction data. The diameter of the cluster is close to 0.71 nm, i.e. the value given by the positions of the carbon atoms on the C 60 shell, and not influenced by their Ti-electron lobes. The studies have revealed the nanometric defect structures in the C 60 lattice which are found consistent with the FCC structure. The cage morphology of the buckyballs in the form of hexagons and pentagons forming the well-known icosahedral structure of the C 60 molecule has been resolved in the finest details with bond lengths in a fair accord with the reported data. The resolved structure forming the lattice shows an orientational disorder which has been frozen from a state in which each molecule at the ambient tem perature is undergoing a rotational motion which is uncorrelated with the motion of its neighbour, in conformity with diffraction and NMR results. Various possible causes of retardation and freezing of the rotational diffusion, relevant to the samples studied are discussed which also include the distortions in the carbon cages detected in the present study.