Formation of doubly excited He atoms during scattering of He2+ ions from a clean and oxygen covered Ni(1Â 1Â 0) surface

The formation of doubly excited states of He atoms during collisions of He2+ ions with energies between 60 eV and 1 keV with a Ni(1 1 0) surface is studied via Auger electron spectroscopy. We observe that the electron spectra from autoionization of doubly excited states of 2s2, 2s2p, 2p2 configurations show a pronounced dependence on the coverage of the target surface with oxygen. For a controlled O2 adsorption on the Ni(1 1 0) surface we can explain the resulting changes in the electron spectra by the modification of the work function of the target surface. Thermal desorption and dissolution into the bulk of surface contaminations at elevated temperatures provides an alternative interpretation of recent work where the local electron spin polarization of a Ni(1 1 0) surface was deduced from changes in the electron spectra as function of target temperature.