Electron Capture Processes on Oxidized Surfaces: $H^{-}$ Formation on Mg/${\mathrm{O}}_2$ and Al/${\mathrm{O}}_2$

Electron capture processes on oxygen covered surfaces were investigated on the example of ${\mathrm{H}}^{-}$ formation in ${\mathrm{H}}^{+}$ scattering. A strong increase in ${\mathrm{H}}^{-}$ production occurs with increasing coverage from the submonolayer to oxide formation range. At low coverages these modifications are interpreted as resulting from competing local effects at oxygen chemisorption sites and nonlocal effects corresponding to work function changes. At high coverages scattering on an ionic solid is considered, with capture occurring at ${\mathrm{O}}^{\delta -}$ sites. Strong ${\mathrm{H}}^{+}$ to ${\mathrm{H}}^{-}$ conversion on an oxide provides an interesting method of negative ion production for injection into fusion devices.