Theoretical study of the Debye-Waller factor in surface extended x-ray-absorption fine structure: Influence of an adsorbed monolayer

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Abstract
We calculate mean-square relative displacements which are required for the determination of the Debye-Waller factor in surface extended x-ray-absorption fine-structure spectroscopy. The lattice dynamical model involves central and angular forces treated within the harmonic approximation. The projected density of modes contributing to relative vibrational motion is obtained from a continued-fraction method. Systematic results for mean correlated displacements between first neighbors are presented for the three low-index faces of fcc transition and noble metals: We predict a strong anisotropy between pairs belonging to the surface and pairs with just one surface atom. Finally, in order to get experimental checks of our results, we also study the case of a monolayer of cobalt on the simple faces of copper. The agreement with the existing experimental results for Cu(111) is very good.