A metastable-induced electron spectroscopy study on the process of oxygen adsorption at a Ni(1 1 0) surface

Abstract

The electronic structure of oxygen-adsorbed Ni(110) surfaces has been studied by metastable-induced electron spectroscopy (MIES). Helium metastable atoms are de-excited both at clean and at oxygen-adsorbed Ni(110) surfaces through the process of resonance ionization followed by Auger neutralization (AN). The intensity of electron emission due to AN was increased by lower exposures of oxygen (∼0.5l), which is attributed to an enhanced contribution of sp-state electrons at the Ni surface to the AN process. At moderate exposures of oxygen (1–3l) where the low-energy electron diffraction (LEED) pattern showed (2×1 ) reconstruction, the MIES spectra exhibited an O 2p-induced peak, caused by inter-atomic Auger transition between O 2p and Ni 3d states. With increasing exposure to 4l, the LEED pattern changed to (3×1 ), while the O 2p-induced peak position moved to lower energies. Variations in the local electronic structure of oxidized top-layers of the Ni(110) surface and the process of metastable-induced electron emission are discussed in connection with the oxygen-induced structural change.