The p(2 x 2) as well as the c(2 x 2) structures of sulphur and oxygen on Ni(100) at coverages of 0.25 and 0.5, respectively, were investigated using high-precision low-energy electron diffraction structure analyses. A uniform expansion of the top-most nickel layer with an underlying buckling reconstruction of the second layer was found in all cases. The total amplitude of adsorbate-induced changes of the substrate was roughly proportional to coverage and depended upon the chemical species adsorbed. However, the geometry of the local adsorption cluster (adsorbate plus nearest neighbour atoms in the first and second substrate layers) was almost coverage-independent for both oxygen and sulphur. Nickel atom positions more distant from the adsorbate atom tended to be near that of the clean surface. The results indicated that a model of local reconstruction might be the key to understanding the observed structures. The adatom created a local reconstruction which was largely independent of coverage but depended upon the reactivity of the adsorbed chemical species. It was also shown that this simple model provided a possible explanation for the experimental observation that, unlike the well-ordered oxygen p(2 x 2)-structure at a coverage of 0.25, the adsorption of sulphur at the same coverage led to a streaky p(2 x 2) low-energy electron diffraction pattern; indicating partial disorder.

Adsorbate-Induced Reconstruction of O and S on Ni(100) - a Local Model. W.Oed, U.Starke, K.Heinz, K.Muller: Journal of Physics - Condensed Matter, 1991, 3[S], 223-30