Soft X-Ray Spectroscopic Study of Fullerene Based Transition-Metal Compounds and Related Systems

Abstract: This thesis addresses the electronic and geometric structures of fullerene based transition-metal compounds and other related systems. The formation of TixC60, VxC60 and NbxC60 compounds has been examined by X-ray photoelectron, soft X-ray absorption and emission and spectroscopy techniques, including resonant inelastic X-ray scattering (RIXS). The symmetry and character of the chemical bond of transition metal-fulleride has been determined. A related study of single-walled carbon nanotubes is also presented. The experimental results are compared to predictions based on calculation within a C60Tix(x=1, 2) cluster model using gradient corrected density functional theory. Good agreement between theory and experiment is found with the Ti metal atom coordinated to the six-ring site. The formation of transition metal fullerides is due to hybridization between the orbitals of the transition metal atoms and the C60 orbitals, and the RIXS spectra at the C K edge reveals the symmetry of the chemical bond. X-ray emission spectra of VxC60 and NbxC60 are similar to that of TixC60, suggesting that the chemical bond has the same symmetry in these compounds. These results indicate that the RIXS method provides an excellent basis for the probing of the bonding between metals and organic molecules. Non-resonantly excited X-ray emission spectra of carbon nanotubes are similar to those of graphite. At resonant excitation, however, there are pronounced differences, suggesting that the σ-π hybridization is reflected in the spectra.