Experimental and Theoretical Evidence for a Strong Anisotropy of the Surface Debye-Waller Factor as Determined for a Monolayer of Cobalt on Copper (111) by Surface Extended X-Ray-Absorption Fine Structure

We present here the first determination of the anisotropy of the surface Debye-Waller factor involved in a surface extended x-ray-absorption fine-structure (SEXAFS) experiment. It is deduced by use of relative temperature-dependent amplitude functions for two different polarizations. The mean square relative displacements of atoms are calculated with an elaborate lattice-dynamical model, treated by a continued-fraction technique. The results are in good agreement which shows the ability of SEXAFS as a valuable tool for the study of surface vibrations.