Electronic structure and properties of rhombohedrally polymerized C-60

The valence electronic structure of rhombohedrally polymerized C-60, synthe sized at 6 GPa and 725 degreesC, has been studied using x-ray emission spec troscopy. The C K alpha spectrum of the polymer was found to differ from th at of the C-60 fullerite especially in the high-energy region. The observed spectra were compared to densities of states, calculated using a tight-bin ding approximation for three two-dimensional hexagonal C-60 networks, disti nguished by the nature of intermolecular bonding. Theoretical spectra of th e polymers agree well with experiment and indicate that changes in the vale nce band of C-60 upon polymerization are mainly due to the formation of int ermolecular bonds, and only to a negligible degree due to a distortion of t he C-60 cage. Rotation of C-60 within the hexagonal layer changes dramatica lly the electronic properties of the polymer from a semiconducting behavior for the structure with 66/66 connections to a metallic behavior for a laye r containing C-60 molecules that are linked through 56/65 bonds. The occurr ence of the latter configuration may explain the observed metalliclike in-p lane conductivity of the rhombohedral phase of C-60. (C) 2001 American Inst itute of Physics.