The coverage dependence of the adsorption structures of Cs on Ag(111)

The structures of five different submonolayer commensurate phases of Cs on Ag(lll) have been determined by low energy electron diffraction (LEED). Thi s paper presents the results of two of these studies: for the primitive (2 root 3 x 2 root 3)R30 degrees and (root 7 x root 7)R19 degrees structures w hich form at coverages of 1/12 and 1/7 respectively. The adsorption site wa s found to be the fee hollow in both cases. These structures are accompanie d by a substrate rumple which has the effect of allowing the Cs atoms to pu sh deeper into the substrate. The structures determined here, along with th e earlier structure determinations of three other submonolayer phases, indi cate that the Cs-Ag bond length does not change over the coverage range fro m 1/12 to the monolayer saturation coverage of 1/3. (C) 1999 Elsevier Scien ce B.V. All rights reserved.