PHOTOEMISSION AND ELECTRON-ENERGY-LOSS-SPECTROSCOPY STUDY OF C-60 MONOLAYERS ADSORBED ON CS-PRECOVERED AU(110) AND OF BULK DISTILLED CSXC60

The adsorption of C-60 in submonolayer and monolayer coverages on Cs-p recovered Au(110) has been investigated by photoemission and high-reso lution electron-energy-loss spectroscopy. Complete fullerene monolayer s display discrete molecular oxidation states of approximately -3, -4, and -6 in the presence of Cs. The oxidation states were determined by a comparison of monolayer electronic structure and vibrational mode f requencies with those of the bulk fullerides. There is no evidence for oxidation states of -2 and -5. Surface-specific measurements on bulk vacuum distilled alkali-fulleride samples showed a strong similarity b etween 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 C-60 Wit h an oxidation state of -3, which may be a useful precursor in produci ng a metastable fee 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 spectros copy of submonolayer C-60 in the presence of multilayers of Cs indicat es that filling of the lowest unoccupied molecular orbital (LUMO)+1 st ates occurs. Completion of the monolayer results in extra charge occup ying the LUMO band only. However, LUMO+1 occupation can also be brough t about by sandwiching complete fullerene monolayers between Ca layers .