The adsorption site of N and O on Ni(100) for a c(2 x 2) overlayer was determined by X-ray-absorption fine-structure measurements. The O atoms adsorbed in the fourfold hollow site on the unreconstructed surface with an O-Ni distance of R1 = 1.97Å and d⊥ = 0.88Å above the first Ni layer. The N atoms also occupy a fourfold hollow site with a bond length of R1 = 1.89Å but the nearest Ni atoms were rotated by a tangential displacement of 0.68Å, such that d⊥ = 0.11Å. The differences in the bonding of N and O were linked to the occupation of their 2p levels.

Structural Determination of an Adsorbate-Induced Surface Reconstruction - p4g(2 x 2)N versus c(2 x 2)O on Ni(100). L.Wenzel, D.Arvanitis, W.Daum, H.H.Rotermund, J.Stöhr, K.Baberschke, H.Ibach: Physical Review B, 1987, 36, 7689-92