Ultrathin films of lead oxide on gold: Dependence of stoichiometry, stability and thickness on O2 pressure and annealing temperature

Ultrathin oxide films grown in vacuum are important in many industrial areas, including microelectronics and heterogeneous catalysis. In this paper, the dependence of oxide stoichiometry, growth kinetics, thickness and stability on O2 pressure and annealing temperature are explored using a high-stability quartz-crystal microbalance and Auger spectroscopy, for the oxidation of lead on gold as a model system. The oxide thickness increases abruptly at specific values of the O2 pressure, as explained previously using Gibbs free energies. A qualitative difference is found between lead-oxide films which are 1 monolayer thick and those which are 2 or more monolayers thick; the former apparently involve exclusively chemisorbed oxygen and can be oxidized and reduced reversibly using thermal oxidation/annealing cycles, whereas the latter involve an extended lead oxide, are more thermally stable, and have a smaller electron inelastic mean free path. Accurate values of the O2 sticking probability are obtained.