The structure of overlayers. III. Nitrogen on Mo {001}

Abstract

The Mo {001} c (2 × 2) - N structure formed upon adsorption of a monolayer of nitrogen on a clean Mo {001} surface is studied by means of low-energy electron diffraction (LEED). Diffracted intensities for a large number of integral-order and half-order beams are calculated with the layer KKR method for different structural models and compared with extensive experimental data. Best overall agreement between calculated and observed LEED spectra is found for a model in which N atoms are adsorbed in the four-fold pyramidal hollows formed by four adjacent Mo atoms on a net consistent with c (2 × 2) symmetry. However, the fit between theory and experiment is good only for certain beams, much less good for others. Attempts at improving the fit by varying the values of structural and non-structural parameters used in the calculations have not been succesful. We raise the question of the significance of a structure model for which the fit with experiment is wholly satisfactory only for certain beams. © 1975.