Scanning Tunneling Spectroscopy and Electronic Properties of Single Fullerene Molecules

Abstract

The discovery of an effective preparation procedure for obtaining macroscopic quantities of C60, a third form of carbon besides graphite and diamond, has triggered a significant research effort to understand the physical and chemical properties of C60 and C60-related fullerene molecules [1]. Fullerene molecules are closed cage molecules containing only hexagonal and pentagonal faces. Chemically stable, cage-structured C60 molecules form an interesting new family of adsorbates on surfaces. They differ significantly from the elemental or simple molecular adsorbates because of their three-dimensional character on the atomic scale. A unique fundamental property of this type of adsorbate is molecular orientation with respect to the host substrate. When an isolated molecule ceases its rotational motion on a surface, it may, in general, adopt a number of binding configurations and hence a range of different orientations. Interaction between molecules could yield still other orientational arrangements. Understanding site- or orientation-dependent C60-substrate interactions therefore lies at the heart of the design of new catalysts with functionalized cage molecules or the fabrication of thin films with desirable orientational orders. However, most surface analysis techniques (e.g., HREELS, PES) can only provide statistically averaged results rather than spatially resolved results.