X-RAY STANDING-WAVE STUDY OF ALKALI-METAL SILICON INTERFACES

We have investigated the adsorption of Rb and Cs on high-symmetry Si f aces ((100)2x1, (111)7x7, (110)16x2 and (211)2x1) using the x-ray stan ding wave technique. Several substrate Bragg reflections were employed to locate the adsorbate using a triangulation method. Hollow-type sit es are preferred at coverages close to saturation, although adsorbate- adsorbate interactions play an important role in some cases, and give rise to a coverage-dependent adsorption site change. In particular, in the cases of Si(111) and Si(211) the adsorption site changes with cov erage (threefold hollow at saturation and on top at low coverages).