Surface structure and composition of Pd8Ni92(1Â 1Â 1): A dynamic LEED study

The Pd8Ni92(1 1 1) surface was studied using low-energy electron diffraction (LEED). IV spectra collected close to normal incidence were analysed by dynamical tensor LEED. Composition and interlayer spacings were determined for first four atomic layers. The surface slab is found to be enriched in Pd (30% in total against 8% in bulk) but this extra palladium is irregularly distributed over the four topmost layers. Contrary to previous reports, the palladium amount, as compared to the bulk, is not significantly changed in the surface layer and it is enriched to 20% only in the third layer. The detected contractions of interlayer spacings are all but one (d34) within the error limits of no contraction at all. We also discuss some aspects of correlations between the fit parameters.