ELECTRON-STIMULATED DESORPTION STUDY OF THE MGO(100)-D2O SYSTEM

A study of the MgO(100)-D2O system at 300 K by electron stimulated des orption (ESD) over the energy range up to 600 eV is presented. Auger e lectron spectroscopy is used as a complementary technique. ESD of the nearly perfect clean surface shows O+ desorbed ions as the main desorb ed species with small amounts of H+ and F+ contaminants. The adsorptio n of D2O produces a dramatic decrease of the O+ intensity in the ESD s pectrum and new signals corresponding to D+ and OD+ ions are observed. There is a first energy threshold at about 30 eV for D+ and H+ desorb ed ions and a second one at 55 eV for O+ desorbed ions. The desorption of these ions corresponds to a primary excitation of the O 2s (24 eV) and Mg 2p (55 eV) core levels, respectively. The ion kinetic energy d istribution of the desorbed O+ ion from the clean surface has two peak s at energies of 6 and 9 eV. The ion kinetic energy distribution of th e D+ desorbed ions also shows a bimodal structure with most probable k inetic energies of 3 and 6.5 eV at 150 eV incident electron energy. Th e ion kinetic energy distribution of the H+ desorbed ions from the H c ontamination correlates quite well with that of the D+ desorbed ions b oth in shape and in energy. The most probable kinetic energy of the OD + is about 3 eV. From these experiments, we propose an adsorption mode l with the D2O dissociated as OD+D. The D species bonds to O surface i ons to form OsurfD radicals, and the OD species bonds to Mg surface io ns. Since the experiments were performed at D2O constant pressure ther e is a large increase of the D+ intensity due to ESD of the D from OB species. The final equilibrium of the adsorbed species is a consequenc e of the D2O adsorption and ESD desorption rates. (C) 1997 American Va cuum Society.