The electronic structure of ${\mathrm{C}}_{60}$ 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 ${\mathrm{C}}_{60}$ films the peaks derived from the top two occupied molecular orbitals are not narrowed but broadened by 0.3 eV in comparison with solid ${\mathrm{C}}_{60}$. This indicates that the delocalization of electrons in the top two π bands is weak, and the peak widths do not reflect the true band dispersion. For approximately one monolayer (ML) of ${\mathrm{C}}_{60}$ 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 ${\mathrm{C}}_{60}$ film. The bulk-plasmon-loss peak, which is 28 eV below the main peak for thick ${\mathrm{C}}_{60}$ films, was not observed for ${\mathrm{C}}_{60}$ films with coverages θ<2 ML. This means that the 28-eV-energy-loss feature is due to a bulk plasmon associated with the solid ${\mathrm{C}}_{60}$ but not with a single ${\mathrm{C}}_{60}$ molecule.

• Received 21 September 1992

DOI:https://doi.org/10.1103/PhysRevB.47.13830