Photoemission Spectroscopy of CARBON(60) and Other Clusters

Photoemission spectroscopy of valence and core levels was used to study the electronic properties of C _{60} and other clusters. Investigations were conducted into the details of the effects of interactions between C_{60} molecules and several different materials, including bonding and charge transfer from surfaces to C_{60 } molecules, in conjunction with in-situ Raman scattering. A systematic investigation of the interaction of C_{60} with substrates of the noble metals Ag, Cu, and Au showed variations in the charge state of an adsorbed C_{60 } molecule with substrate work function. The strongest degree of charge transfer occurred from the Ag substrate, and a moderate amount was seen for the Cu substrate. While no charge transfer was seen for Au, there were indications of interactions between the substrate and C_ {60} molecules. Further studies of the surface interactions of C_{60} utilized Bi or Ge substrates. The Bi system showed signs of charge transfer to the LUMO-derived band near E_{rm F}, with no charge transfer observed for either Bi or Ge when deposited on C_{60} films. A strong initial shift of spectral features to lower binding energy was observed for C_ {60} deposited on Ge, which shifted to bulk values as the C_{60} thickness increased. This is additional evidence that the more reactive rough Ge surface is influencing the C _{60} molecules by means of the dangling bonds. The electronic states of alkali metal-doped C _{60} films showed a number of unusual properties. An additional valence-level band in the region near the LUMO-derived band was observed in PES spectra of ultrathin alkali metal-doped C_ {60} films. A corresponding Raman feature correlates well with this band as it changes with temperature and charge transfer. HREELS spectra of C_ {60} and alkali metal-doped C _{60} films were also measured. For thin films of rm Na_3C_{60 }, changes in the photoemission spectra showed increased metallic behavior with increasing temperature. There is a significant increase in the density of states at the Fermi energy with temperature, either from thermally induced effects or structural changes.