Sharp high-resolution Si2pcore level on the Sb-terminated Si(111) surface: Evidence for charge transfer

An $\mathrm{S}\mathrm{b}/\mathrm{S}\mathrm{i}(111)\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ surface has been studied by high-resolution core-level spectroscopy. All the components of the Si $2p$ core level related to the clean surface have disappeared, and one strong Sb-induced component could be identified at a binding energy +0.13 eV with respect to the bulk peak. Such a component is mainly due to charge transfer between Si atoms at the top layer and Sb trimers. Two more small components are observed: one at +0.29 eV, due to Sb atoms residing at a different position, and one at -0.14 eV, due to local disorder. On the Si $2p$ core level taken in bulk sensitive mode, we found a very narrow bulk component with a total full width at half maximum of 140 meV at $T=100\mathrm{K}.$