The Ni(100) surface reconstructed upon adsorption of half a monolayer of nitrogen. The reconstructed phase consisted of a c(2 x 2) overlayer of nitrogen with a clockwise and counter-clockwise rotation of the nickel surface atoms around two nearest neighbour nitrogen atoms, respectively. The same p4g(2 x 2) reconstruction was also observed with carbon overlayers. Total energy calculations and lattice dynamic analysis have shown that this reconstruction was driven by internal stresses caused by a repulsive interaction between the first layer nickel atoms. Measurements were made of the phonon dispersion branches of the p4g(2 x 2) nitrogen-covered surface along the [110] direction. Two adsorbate induced phonon branches above the bulk phonon branch of nickel were found. The branches were similar to those found for the carbon covered surface and indicate that nitrogen sits close to the surface in the fourfold hollow site. In addition to the adsorbate associated modes surface resonances inside the bulk band and the Rayleigh phonon were measured. The various modes were identified by comparing experimental results to lattice dynamical calculations.

Surface Phonon Dispersion and Adsorbate Induced Reconstruction of Ni(100). W.Daum, S.Lehwald, H.Ibach: Surface Science, 1986, 178[1-3], 528-36