Structures of oxygen-covered Ni(110) surfaces

The structures of oxygen-covered Ni(110) surfaces have been studied at 300 K by the in situ combination of low-energy electron diffraction (LEED), high-resolution electron-energy-loss spectroscopy, Auger electron spectroscopy, and work-function-change measurement. The electron-energy-loss peaks due to the excitation of the nickel-oxygen stretching vibration have been observed at 480, 380, and 444 ${\mathrm{cm}}^{-1\mathrm{}}$. The 480-${\mathrm{cm}}^{-1\mathrm{}}$ peak is associated with the oxygen atoms in the short-bridge sites of the unreconstructed Ni(110) surface, the 380-${\mathrm{cm}}^{-1\mathrm{}}$ peak with the oxygen atoms which lie in the bridge sites of the Ni[001] rows of the reconstructed surface, and the 444-${\mathrm{cm}}^{-1\mathrm{}}$ peak with the nickel oxide patches. It is proposed, when the LEED (2×1) pattern is seen, that two structures, i.e., the unreconstructed and reconstructed (2×1)-O structures, are formed. The structures of the "initial"-(3×1)-O, (3×1)-O, (9×4) and disordered-nickel-oxide surfaces are discussed. Experimental results and discussion on the "Ni(110) (2×1)-O" surfaces produced by high-temperature heating are included.