XPS CHARACTERIZATION OF ULTRA-THIN MGO FILMS ON A MO(100) SURFACE

The oxidation of ultra-thin Mg films supported on a Mo(100) surface has been studied using X-ray photoelectron spectroscopy (XPS) in the 90-1300 K sample temperature range. Upon adsorption of oxygen onto Mg thin films or deposition of Mg in the presence of oxygen, a Mg(2p) XPS feature at approximately 50.5-50.8 eV is observed. The binding energy of this peak is higher than that of metallic Mg(2p) (at 49.6 eV) and is assigned to oxidized magnesium. The associated O(1s) XPS spectra exhibit two peaks which can be attributed to a dioxygen species concluded to be magnesium peroxide and the lattice oxygen in MgO. Upon annealing the peroxide containing film to approximately 700 K, the magnesium peroxide is reduced to MgO through the loss of oxygen and metallic magnesium existing within the film is subsequently oxidized to MgO. Mg deposition in an oxygen background (approximately 10(-6) Torr) onto the Mo(100) surface at 300 K produces essentially stoichiometric MgO films.