Final-state pseudopotential theory for the Ge 3d core-level shifts on the Ge/Si(100)-(2×1) surface

We have calculated the Ge 3d core-level shifts on the Ge/Si(100)-(2×1) surface using the final-state pseudopotential theory. We find that the core levels of the up and down atoms within the asymmetric Ge dimer are separated by 0.54 eV at 1-ML Ge coverage, 0.43 eV at 2-ML Ge coverage, and 0.40 eV at the clean Ge(100) surface. Such a large core-level shift represents a substantial charge asymmetry within the Ge dimer. The present results agree well with recent x-ray photoemission spectroscopy (XPS) data on the Ge(100) surface, but disagree with XPS data on the adsorbed Ge/Si(100) surface.