Study of the electron damage of the MgO(100)-D2O system by ESD

An electron-stimulated desorption (ESD) study of electron damage of a D2O layer adsorbed on the MgO(100) surface at room temperature is presented. After exposing the surface to D2O, the surface spectrum shows the main ESD component to be D+ ions, with lower intensity signals corresponding to O+ and OD+ ions. When the surface is simultaneously exposed to heavy water and electron bombardment, there is a rapid initial increase of the D+ intensity accompanied by a decrease of the intensity of the O+ ions. Electron damage of the surface after exposing to D2O produces a significant decrease of the D+ intensity, while the O+ and OD+ intensities decrease more slowly. Heavy water adsorption does not change the form of the ion kinetic energy distribution of the O+ ions with electron dose, except for a decrease in intensity. Electron damage increases the intensity of the ion kinetic energy distribution of D+ again without changing its shape. These experiments show that heavy water adsorption under electron bombardment does not induce any chemistry of the adsorbed species, but enhances the fragmentation rate of the OD species which, in turn, increases the yield of D+ ions. Values of total desorption cross-sections for the three ions species are reported. (C) 1997 Elsevier Science B.V.