Stoichiometry-Dependent Chemical Activity of Supported MgO(100) Films

International audience; Here we show that the stoichiometry and, consequently, the chemical activity towards hydroxylation of MgO(100) films grown by reactive deposition on Ag(100) strongly depends on the O 2 partial pressure during film growth. Oxygen-deficient films undergo dramatic relative oxygen uptake either by exposure to a partial pressure of water vapor or by aging in vacuum for a sufficiently long time. Conversely, on stoichiometric monolayer MgO islands, photoemission analysis of the O 1s level and scanning tunneling microscopy images are consistent with the prediction that dissociative adsorption of water occurs only at the borders of the islands.