Molecular adsorption characteristics of lanthanum oxide surfaces: the interaction of water with oxide overlayers grown on Cu(111)

The adsorption of water on both disordered-polycrystalline and ordered-epitaxial layers of lanthanum oxide grown on a Cu(111) substrate has been studied using XPS, UPS, TPD and molecular beam measurements. In all cases, the main interaction at 300 K is dissociative, leading to extensive surface hydroxylation, and the dissociative sticking probability is close to unity, provided that the oxide film fully covers the underlying copper substrate. The extent of uptake indicates the formation of a saturated surface layer of hydroxyl groups on A-form La2O3 (001)-type terraces, and enhanced adsorption at cationic sites of lower coordination. The water may act as an oxidising agent on oxygen-deficient films, but otherwise the recombination of surface hydroxyl groups upon heating leads to molecular desorption over the temperature range 400–700 K and regeneration of the clean oxide surface.