Observation Of The Development Of The Electronic-Structure Of C(60) Films From Submonolayer Coverage To 2 And 3 Dimensionality

The electronic structure of C60 films deposited on Sn substrates has been studied by UV and x-ray photoemission spectroscopy. In contrast with the tight-binding approximation, for submonolayer amounts of C60 films the peaks derived from the top two occupied molecular orbitals are not narrowed but broadened by 0.3 eV in comparison with solid C60. This indicates that the delocalization of electrons in the top two pi bands is weak, and the peak widths do not reflect the true band dispersion. For approximately one monolayer (ML) Of C60 film, x-ray photoemission studies of C 1s core levels reveal a feature centered at 22 eV below the main peak. Analyses show that this feature is caused by the plasmon loss of the two-dimensional C60 film. The bulk-plasmon-loss peak, which is 28 eV below the main peak for thick C60 films, was not observed for C60 films with coverages theta < 2 ML. This means that the 28-eV-energy-loss feature is due to a bulk plasmon associated with the solid C60 but not with a single C60 molecule.