The geometric structure of Rb/Cu(111) investigated with X-ray standing waves: Rb coverage dependence

We have carried out a back reflection X-ray standing wave (BRXSW) investigation of the geometric structure and degree of ordering of the system Rb/Cu(111) as a function of Rb coverage. We observe no change in the Rb-Cu(111) perpendicular spacing as a function of coverage from saturation coverage of theta = 1/4 down to a coverage of theta = 1/16. We find a high degree of ordering of the Rb atoms perpendicular to the surface at all coverages, but a very low degree of order parallel to the Cu(111) surface. No differences in our results were detected for measurements at room temperature versus at similar to 190 K.