The clean and H-induced reconstruction of W(100) studied by LEED at slanting primary bean incidence

Abstract

We present a new LEED study of the clean and hydrogen induced c(2×2) reconstruction of W(100). We show that the LEED intensity analysis for data taken at sufficiently oblique incidence (θ≈74°) provides high sensitivity for surface parallel parameters without loosing that for coordinates normal to the surface. This allows the quantitative proof of the zig-zag model for the clean surface and that of the dimer model for the hydrogen covered phase. The reconstruction amplitude within the first tungsten layer is almost the same for both phases, i.e. 0.210±0.040 Å for the clean surface and 0.235±0.045 Å for the hydrogen induced reconstruction. The contraction of the first layer distance reduces slightly from (6.0±1.6)% to (4.5±2.5)% as commonly observed as an effect of hydrogen adsorption. This proves that the dominant impact of hydrogen adsorption of c(2×2)W(100) is to induce a symmetry switch of the surface reconstruction.