The structure of Ni(100)-c(2x2)-Na: A LEED analysis

The structure of Ni(100)-c(2X2)-Na has been investigated by analysis of extensive new low-energy electron-diffraction (LEED) data. The structure is found to contain Na atoms adsorbed in fourfold hollow sites on an unreconstructed and essentially unrelaxed substrate. The Na-Ni layer spacing is 2.38+/-0.04 Angstrom and the first Ni-Ni layer spacing is 1.75+/-0.01 Angstrom. These results are in good agreement with the conclusions of an early study by Demuth et al. [J. Phys. C 8, L25 (1975)]. Good agreement between experimental and calculated LEED intensities is obtained using the dynamic theory of LEED, with a conventional, muffin-tin potential for the adsorbed Na atoms and a step potential at the surface. The good agreement pertains not only to the energy positions and relative intensities of peaks in intensity-energy spectra for the diffracted beams, but also to the relative beam intensities, which span a range of nearly two orders of magnitude.