Normal-incidence standing X-ray wavefield absorption and SEXAFS studies of adsorption structures on Cu and Ni surfaces

The relative insensitivity of the Bragg condition to the exact angle of incidence to the scattering plane near normal incidence means that the X-ray standing wavefield absorption method can be applied to typical (imperfect) surface-science single-crystal samples in this special geometry. The method is highly complementary to the SEXAFS experiment that can be performed with the same instrumentation and we demonstrate this with examples of structures associated with Cl, CH3S— and S on Cu(111) and Hg on Ni(100). The combined approach is particularly valuable in cases in which the adsorbed species induce substrate reconstruction, and in particular reasonably definitive structures of considerable complexity have been identified for the two S-containing surfaces.