LEED structure analysis of p(√3 × √3)R30°-O/Ni(111)

Abstract

The p(√3 × √3)R30 ° structure formed by oxygen adsorption on Ni(111) at coverage θ = 0.33 was investigated by LEED intensity measurements and their full dynamical analysis. Oxygen is found to reside on threefold coordinated fcc hollow sites at height 1.08 ± 0.02 Å above the substrate with a Ni-O bondlength of 1.80 ± 0.02 Å. Compared to the unrelaxed clean surface, which was also analysed, the topmost nickel layer spacing is slightly expanded to 2.05 ± 0.02 Å (bulk value: 2.03 Å) whereas the second to third interlayer spacing is practically unrelaxed (2.02 ± 0.02 Å). A lateral reconstruction of the first substrate layer as found for the p(2 × 2) phase can be ruled out, i.e., lateral atomic shifts must be smaller than the error limit of 0.03 Å. Vertical buckling in the first substrate layer is excluded by symmetry. This means that the reconstruction of the p(2 × 2) phase is lifted in the transition p(2 × 2)→ p(√3 × √3)R30°, i.e., by a coverage increase from θ = 0.25 to θ = 0.33. The quality and reliability of the structure determinations are mirrored by a Pendry R-factor of R = 0.16 for both the clean and oxygen-covered surface.