MULTISITE OCCUPANCY AT THE ALKALI SILICON(111) INTERFACE STUDIED WITH XSW

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