Physical interaction between tip and molecules in scanning force microscopy imaging of adsorbed C60 and fullerene tubules

Abstract

After the discovery of C60, a large family of fullerene molecules was also identified. Among them, elongated fullerenes are formed by the tubular assembly of carbon atoms. The van der Waals bonds between fullerene molecules are due to the correlations between fluctuating charge densities inside the molecules. The interaction is then dominated by collective excitations which are sensitive to the shape of the molecules. Therefore, van der Waals attraction is expected to be modified when considering successively spherical C60, C70 and more elongated fullerenes (tubules). This paper presents self-consistent computations of the van der Waals interaction between a (111) diamond probe tip and various fullerene molecules adsorbed on a gold surface. Relative to spherical C60, the dependence law of the force experienced by the probe tip as a function of the tip-sample distance decreased when approaching fullerene tubules. Simulations of scanning force microscope scans of carbon tubules next to C60 molecules show that the shape of the molecules affects the interpretation of scanning force microscopy imaging. Particularly, information about the height of the various molecules deposited on the surface must be considered with some care since carbon tubules with the same radius as C60 interact more strongly with the probe tip.