Observations of coexistence of FCC and HCP phases in C60 by HREM

Since the discovery of a large scale synthesis of fullerenes there has been intense interest in the structure of these materials. The first diffraction data suggested that crystalline C60 had a hexagonal close-packed (hep) structure with a nearest neighbor distance of 10.04 Å. The possibility of a disordered stacking of C60 molecules was first noted in this study. Since then, there has been some confusion regarding the exact crystalline structure of C60 as determined by electron and X-ray diffraction. In particular, a diffraction feature corresponding to a spacing of 8.7 Å has been noted in several studies. Recendy there had been a growing consensus that fcc is the correct structure for sublimed C60. Although the internal carbon atom arrangement of the C60 molecules cannot be determined, the actual packing and defects in C60 crystals over small and relatively large regions are readily seen by HRTEM. We have found by direct imaging a relatively large region of defect-free hep packing of C60 spheres sublimed onto a relatively cool microscopy grid.