X-RAY PHOTOELECTRON DIFFRACTION IN THE BACKSCATTERING GEOMETRY - A KEY TO ADSORPTION SITES AND BOND LENGTHS AT SURFACES

For a well-characterized (2 x 1)-1O adsorbate phase of oxygen on rhodi um (II I) we have identified photoelectron interference fringes in the backscattering geometry for O Is adsorbate emission at 723 eV kinetic energy. Although these features are weak, they show up as characteris tic rings covering large regions of the full hemispherical photoelectr on diffraction pattern. They represent the situation of a simple two-a tom electron interferometer and yield directly the most relevant infor mation on the adsorbate geometry such as the adsorption site, the adso rbate-substrate bond length, and the bond angle. [S0031-9007(98)06936- 1].