STRUCTURAL STUDY OF RH(100)-C(2X2)-S USING THE NORMAL-INCIDENCE STANDING X-RAY WAVE-FIELD METHOD

The adsorption site for sulphur in the Rh(100)-c(2 x 2)-S system has b een investigated using the normal-incidence standing X-ray wavefield a dsorption (NISXW) technique. Two Bragg reflecting planes were used for the measurements, the (200) plane (parallel to the surface) and the ( 111) plane (inclined 54.7 degrees to the surface). The distance betwee n the S atoms and the surface plane was found to be 1.38+/-0.05 Angstr om. The adsorption site was determined by triangulation of the distanc es between the S atoms and the (200) and (111) planes, coupled with co mparison of the measured coherent fractions with calculations of the e xpected values. The results indicate that S adsorbs in the symmetric f our-fold hollow site, as found for S adsorption on other fcc(100) surf aces.