Ultrathin nickel oxide films grown on Ag(001): a study by XPS, LEIS and LEED intensity analysis

The structure of a nickel oxide film 2 ML thick has been investigated by LEED intensity analysis. The NiO film was prepared by evaporating Ni in presence of O-2 at a pressure in the 10(-6) mbar range. The growth of the oxide film was followed by XPS, LEIS and LEED. In the early stages of deposition, the film shows a (2 x 1) superstructure in LEED. After deposition of 2 ML of NiO, a sharp (1 x 1) LEED pattern is observed. The intensity versus electron energy curves of the LEED spots were measured for this NiO(I x 1) film and analysed by means of the tensor LEED method. A good level of agreement of the experimental LEED intensities with those calculated for a pseudomorphic NiO(0 0 1) film was obtained. We found that oxygen atoms at the oxide-substrate interface are on-top silver atoms. The interlayer distance in the oxide does not differ significantly from that in bulk NiO(0 0 1), within the accuracy of the analysis. An outward displacement (0.05 +/- 0.05 Angstrom) of oxygen atoms with respect to nickel atoms was found at the oxide film surface. The interlayer distance at the silver-nickel oxide interface is 2.43 +/- 0.05 Angstrom. (C) 2003 Elsevier Science B.V. All rights reserved.