Surface relaxation inc(2×2)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(2×2)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° of the Ni(100) crystal employed, and the Cl K fluorescence yield spectrum revealed that Cl atoms are located 1.80±0.03 Å above the Ni(200) lattice plane. On the other hand, the SEXAFS results elucidated that the Cl-Ni layer spacing is 1.60±0.02 Å. Combining these data, it was found that the surface nickel layer relaxes outward by 0.20±0.05 Å (11% of the bulk spacing).