The results of an X-ray standing wave study of the (111) 7 x 7 interface as a function of (Cs, Rb) coverage were reported. The 3-fold hollow site, the 3-fold filled site and all of the dangling bond sites (atop, adatoms and vacancy) were considered to be available sites for the adsorbate at the surface. Although measurements were made only for the (111) and the (¯111) diffracting planes, and the number of sites was quite high, well-defined distributions of the occupancy probabilities in the various sites for each sample could be found by deducing the adsorbate-substrate bond length and the substrate atomic coordinates of the reconstructed surface. The results indicated the occurrence of a relaxation of the substrate atoms under the 3-fold hollow and 3-fold filled sites.

P.Castrucci, S.Lagomarsino, F.Scarinci, C.Giannini: Journal of Physics D, 1993, 26[4A], 192-6