Kinetics of CO adsorption on epitaxial (111)Cu on (111)Pd thin films

Abstract

CO adsorption has been studied on (111)Cu/Pd thin-film surfaces grown epitaxially on mica in UHV of base pressure 5×10−11 Torr. Auger electron spectroscopy investigations of the growth of Cu on (111)Pd films showed that layer growth occurred. The Kelvin probe, work function method was used to monitor the CO adsorption at 298 K as a function of Cu overlayer thickness. It was found that very thin Cu overlayers had a drastic effect on saturation CO coverage: one monolayer of copper reduced the saturation CO coverage by ∼95%. For the pure (111)Pd thin-film surface, the data showed that the rate of CO adsorption changes when the CO fractional coverage approaches ∼0.4. This result is most likely due to the previously reported change in CO superlattice structure that occurs with increasing coverage. The kinetic adsorption data for various bilayers were interpreted in terms of a first-order Kisliuk mobile precursor model.