ADSORPTION SITES OF RB AND BR ON THE SI(100)2 X-1 SURFACE

The interfaces Rb/Si(100)2 x 1 and Br/Si(100)2 x 1 have been investigated by using X-ray standing-wave fields. The adsorption distance from the [400] bulk lattice plane was measured for different adsorbate coverages and annealing temperatures. Br atoms saturate the free dangling bonds of the 2 x 1 surface. In the case of Rb, a multi-site situation (pedestal and valley sites) is observed at room temperature for coverages of one monolayer. After surface annealing, adsorption on one site is promoted. For adsorption on symmetric dimers, this site is the cave one. In the case of adsorption on buckled dimers, the on top site would also be compatible with the results. A differentiation between both situations is not possible on the basis of our data.