MULTISITE OCCUPANCY AT THE ALKALI SILICON(111) INTERFACE STUDIED WITHXSW

In this paper we report the results of an x-ray standing wave (xsw) st udy of an Si(111) 7 x 7-alkali metal (Cs,Rb) interface as a function o f coverage. The three-fold hollow (H-3) site, the three-fold filled (T 4) site and all the dangling bond sites (atop, adatoms and vacancy) ha ve been considered as available sites at the Si surface for the adsorb ate. Although measurements have been recorded only for the (111) and t he (111BAR) diffracting planes and the number of sites is quite high, well defined distributions of the occupancy probabilities in the diffe rent sites f(i) for each sample, can be found assuming the adsorbate-s ubstrate bond length and the substrate atomic coordinates of the recon structed surface. Our results indicate a relaxation of the substrate a toms under the H-3 and T4 sites.