Electron capture and loss processes on oxides and oxidised surfaces

Electron capture and loss processes on MgO (1 0 0) and oxygen covered Mg and Al surfaces are studied on the example of formation and destruction of H-, O- and F- in atom/anion scattering. Electron capture is demonstrated to occur very efficiently on MgO (1 0 0) and can be understood in terms of a localised non-resonant capture mechanism between the incident atom and a lattice O anion. Electron loss from incident negative ions is observed and is attributed to loss to the conduction band. Changes in capture rates on oxygen covered surfaces are studied from the limit corresponding to chemisorption to oxide film formation. Ln the chemisorption range capture is attenuated because of changes in the local density of states (LDOS) and in the positions and widths of the anion level near the adsorbate. (C) 1998 Elsevier Science B.V.