Scanning tunnelling microscopy of solid C60/C70

THE detection of a strong peak in mass spectra of carbon vapour corresponding to a cluster of 60 carbon atoms led to the proposal that these clusters corresponded to highly symmetric C60 molecules in the shape of truncated icosahedra. Recently macroscopic quantities of C60 and the related species C70 (thought to have an elongated cage structure) have been prepared and purified in a solid form, called fullerite. The availability of a solid form has made possible studies using infrared and ultraviolet-visible absorption spectroscopy, X-ray and electron diffraction, NMR and Raman spectroscopy, all of which provide evidence that supports the proposed 'soccer ball' structure of C60. Here we report the direct imaging of C60 molecules in sub-micrometre-sized particles of fullerite, using scanning tunnelling microscopy. The images reveal spherical molecules, spaced about 1 nm apart, stacked in close-packed arrays. Our results give a direct demonstration of the highly symmetric structure of these clusters.