Helium Diffraction from Oxygen-Covered Nickel Surfaces

Helium atom diffraction results are presented for oxygen-covered Ni(001) and Ni(110) surfaces. For 0/Ni(001) the diffraction data has clearly favored a single vertical distance for oxygen chemisorption in both the p(2 × 2) and c(2 × 2) phases. This conclusion now seems to be quite generally accepted. For 0/Ni(110) there are several competing candidates which include among others the missing row and the saw-tooth model. We have carried out simple model theoretical calculations based on the Esbjerg-Nørskov-Lang relation between the surface charge density and helium-surface repulsive potential. We have used atomic Hartree-Fock charge densities to generate surface charge densities. The corrugation coefficients have been calculated for various geometrical configurations of oxygen on Ni. These results are compared with the experimental data in order to deduce information about the chemisorption of oxygen on Ni(110).