Photoemission and electron-energy-loss-spectroscopy study of C60 monolayers adsorbed on Cs-precovered Au (110) and of bulk distilled CsxC60

The adsorption of C60 in submonolayer and monolayer coverages on Cs-precovered Au~110! has been investigated by photoemission and high-resolution electron-energy-loss spectroscopy. Complete fullerene monolayers display discrete molecular oxidation states of approximately 23, 24, and 26 in the presence of Cs. The oxidation states were determined by a comparison of monolayer electronic structure and vibrational mode frequencies with those of the bulk fullerides. There is no evidence for oxidation states of 22 and 25. Surface-specific measurements on bulk vacuum distilled alkali-fulleride samples showed a strong similarity between the properties of the single-layer films and the surface layers of the bulk material. Annealing experiments demonstrated that it was possible to produce a well-ordered, close-packed monolayer of C60 with an oxidation state of 23, which may be a useful precursor in producing a metastable fcc Cs3C60 film by epitaxial growth. Bonding with the substrate stabilized this film with respect to bulk samples leading to desorption only at temperatures .900 K. Electron-energy-loss spectroscopy of submonolayer C60 in the presence of multilayers of Cs indicates that filling of the lowest unoccupied molecular orbital ~LUMO!11 states occurs. Completion of the monolayer results in extra charge occupying the LUMO band only. However, LUMO11 occupation can also be brought about by sandwiching complete fullerene monolayers between Cs layers.