Datensatz

Zusammenfassung

The evolution of core-level photoemission spectra has been studied during the initial stages of Cs and In overlayer growth on thin SiO₂ layers on Si(111) substrates to probe the influence of the metal-SiO₂ interaction on the charge state of the resulting structure. The Si 2p soft-x-ray photoelectron spectra on the SiO₂ and the Si substrate, which have been recorded simultaneously, show substantially different shifts to higher binding energy for the two components of the structure for Cs adsorption on the SiO₂ surface, but only small uniform shifts for In overlayers. The Si 2p core-level spectra have been analyzed by simulating the spectra with a model that separates the Cs-covered SiO₂ structure into thin layers with a constant dipole field gradient applied across them. Accordingly, the metal-induced Si 2p core-level shifts of the Si substrate are interpreted in terms of Si band-bending changes as a result of charge transport from the metal layer to the SiO₂/Si interface. The differential Si 2p shifts, which lead to a larger separation of substrate and oxide peaks on cesiated SiO₂/Si than on the pristine SiO₂/Si structure, are discussed in terms of a Cs-induced dipole field across the SiO₂ layer. It is proposed that the different behavior of Cs and In overlayers may be related to the different electronegativity and, consequently, to the different adsorbate dipoles of the two metals.