INTERACTION OF O-2 WITH LI-AU AND CS-AU FILMS - A PHOTOEMISSION AND THERMAL-DESORPTION STUDY

The reaction of O2 with thick Li-Au or Cs-Au films supported on Ru(001 ) has been investigated using thermal desorption mass spectroscopy and core- and valence-level photoemission. The interaction of O2 with CsA u at 100 K produces O2(2-) (the only oxygen species at low O2 exposure s) and O2-. Annealing of the O2/CsAu film to 300 K leads to the disapp earance of O2- and the appearance of O2 . The adsorption of O2 on Li-A u alloys at 300 K produces the O2- ion together with another oxygen sp ecies. The presence of oxygen shifts the Au(4f) and Cs(3d) levels of C sAu approximately 1 eV toward lower binding energy, with the final pea k positions being very close to those observed for metallic Au and oxi dized Cs. A similar result was observed for O2/Li-Au. No evidence for bonding between the oxygen ions and Au was found. At T less-than-or-eq ual-to 300 K, oxygen breaks the Au-alkali bonds to form Li.O or Cs.O a nd very small Au clusters that are dispersed on the film. Annealing to 500 K produces sintering of these Au clusters into large three-dimens ional particles. The existence of Li-O or Cs-O bonds increases the the rmal stability of the alkali in the film. The Li.O and Cs.O compounds decompose at much higher temperatures than the LiAu and CsAu alloys.