Surface relaxation in c(2 x 2)Cl/Ni(100) determined by the soft-x-ray standing-wave method combined with surface-extended x-ray-absorption fine-structure spectroscopy.

Abstract

The surface structure of c(2\ifmmode\times\else\texttimes\fi{}2)Cl/Ni(100) has been investigated by means of the soft-x-ray standing-wave (SW) method and surface-extended x-ray-absorption fine-structure (SEXAFS) spectroscopy. In the SW experiment, measurements of Ni(200) Bragg reflectivities in the vicinity of normal incidence allowed the determination of the mosaic width of 0.3\ifmmode^\circ\else\textdegree\fi{} of the Ni(100) crystal employed, and the Cl K fluorescence yield spectrum revealed that Cl atoms are located 1.80\ifmmode\pm\else\textpm\fi{}0.03 \AA{} above the Ni(200) lattice plane. On the other hand, the SEXAFS results elucidated that the Cl-Ni layer spacing is 1.60\ifmmode\pm\else\textpm\fi{}0.02 \AA{}. Combining these data, it was found that the surface nickel layer relaxes outward by 0.20\ifmmode\pm\else\textpm\fi{}0.05 \AA{} (11% of the bulk spacing).