X-ray standing wave studies of germanium adsorbed on Si(111) surfaces

The positions of germanium atoms adsorbed on Si(111) surfaces have been determined with X-ray standing waves. Ge atoms have been found to occupy the atop site and/or vacancies in the inner layer of the substrate surface bilayer for the (1 × 1) superstructure. For the (7 × 7) structure, our results support the dimer adatom stacking-fault model of Takayanagi et al. for the bare silicon surface. Ge atoms occupy the surface-atop and the adatom-atop sites on this structure. A higher binding energy for the surface-atop site is indicated from the growth of germanium at different substrate temperatures