Si 2p core-level shifts at the C2H2/Si(001) and C2H4/Si(001) surfaces -: art. no. 193402

Two recent x-ray photoemission spectroscopy (XPS) experiments reported very different Si 2p core-level shifts at the C2H2/Si(001)-2 x 1 [Phys. Rev. B 60, 11 586 (1999)] and C2H4/Si(001)-2 x 1 [Phys. Rev. B 58, 11 029 (1998)] surfaces. However, our initial- and final-state theory calculations show that both systems give the same behavior in the surface core-level shifts: i.e., the chemical shifts of the clean surface are essentailly canceled by the di-a bonding between adsorbed molecules and Si dimer atoms. The present results agree well with the XPS data of the C2H4/Si(001)-2 x 1 surface, but disagree with those of the C2H2/Si(001)-2 x 1 surface.