ADSORPTION-SITE INVESTIGATION OF RB/CU(111) USING THE X-RAY STANDING-WAVE METHOD

We have carried out a back reflection x-ray standing-wave investigation to study the adsorbate-substrate bond length and bonding site for the system Rb/Cu(111). Our low-energy electron diffraction study showed an ordered (2 X 2) phase for one monolayer of Rb on Cu(111) (theta = 0.25). By measuring both the (111) and (111BAR) Bragg reflections at this coverage, we determine the Rb adsorption to be in the top site. We observe a high degree of order in the Rb overlayer perpendicular to the surface, with large disorder parallel to the surface.