O₂ Dissociative Adsorption on Mg(0001)─Surface Oxidation, Peroxide Formation, and Oxide Layer Thickening

O₂ exposure-dependent oxidation process on the <i>p</i>(4 × 4) Mg(0001) surface has been systematically studied based on DFT computation and AIMD analysis. At initial exposure, O₂ dissociates spontaneously, and the oxygen atoms penetrate the subsurface layers, forming oxide islands due to the electrostatic attractive Mg-O interaction. The oxide islands grow laterally and vertically with an increase in the level of exposure to O₂ and eventually, the first two stoichiometrically oxidized layers (32 × O) are formed. The oxidized surface layer can further uptake both oxygen atoms and molecular O₂ and forms stable mixed adsorption configurations (4O+xO₂, x = 1-4), which reveal the formation of surface peroxides, as proposed by an XPS study. The AIMD analysis explains the experimentally observed changes in the LEED patterns during the oxidation process upon the increase of O₂ exposure.