Resonant Soft X-ray Spectroscopic Studies of C60 and Related Materials

Detta är en avhandling från Uppsala : Acta Universitatis Upsaliensis

Sammanfattning: This thesis addresses the electronic structure of molecular and correlated solids using resonant inelastic soft X-ray scattering (RIXS), non-resonant X-ray emission, photoemissionand X-ray absorption spectroscopies. The use of monochromatised synchrotron radiation and improved energy resolution for X-ray emission have made it possible to elucidate the normal state transport properties and to get further insight into the electron-vibration coupling in fullerenes and the related compounds. The latter is particularly important in order to understand the physical mechanism of superconductivity in fullerene materials. The characteristic intermolecular charge transfer times in K3C60 are found to be longer than the X-ray scattering time-scale (a few femtoseconds). The slow intermolecular charge transport emphasizes that the reduced fullerene compounds can not be treated as simple metals, but rather as systems with strong electron correlation. The electron structure and the bonding character of the more covalent transition metal (V, Ti, Nb) fullerides have been addressed. Evidence indicating the existence of chemical bond between the metal atom(s) and C60 is presented, and the nature of the bond is discussed by comparing RIXS spectroscopic measurements and theoretical predictions. The (crystal) momentum conservation is discussed by comparing the spectroscopic data of a quasi-1D (carbon nanotubes) and quasi-2D (graphite) systems. Finally, the intra-atomic electron-electron correlation is discussed in the case of double core-hole state photo-excitation and de-excitation processes. RIXS including intermediate states with two core vacancies has been observed for the first time in the soft X-ray region.