Early nucleation on the Si(001)-2 x 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(001)-2 x 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. (C) 2002 Elsevier Science B.V. All rights reserved.