Early nucleation on the Si(0 0 1)-2×1 surface

The analysis of synchrotron radiation Si 2p core-level photoemission spectra provides fruitful information about the interface structure. A constraint on layer-wise intensities, based on the inelastic mean-free-path, is used to extract the 2p binding energy shifts of the first three outer layers. Both clean and adsorbate-covered surfaces have been successfully analyzed. The results for the clean Si(0 0 1)-2×1 surface, which reflect both the strain due to the reconstruction and changes in final-state screening, are in very good agreement with theory. However, for adsorbate-covered surfaces charge-flow, due to the electronegativity difference between Si and adsorbate atoms, dominates the shifts. Results for prototypical interfaces, with the adsorbates Ge, Cl, and oxygen, are presented.