Pb/Si(1 0 0)2 x 1 surface studied by high resolution core-level photoemission spectroscopy

A Pb/Si(100)2x1 surface has been studied at T=120K by high resolution core-level spectroscopy using a thirdgeneration synchrotron light source. A strong component (S), could be identified at a binding energy (BE) of-0.20 ± 0.01 eV with respect to the bulk peak. This is indicative of some reorganization of the topmost silicon atomsafter Pb adsorption with the formation of Si Pb bonds and Pb Pb symmetric dimers. However, this shift is in theopposite site respect to the bulk peak, as compared with Sb/Si(100)2x1, thus suggesting the interplay of final statesscreening effects and charge transfer in the core-level position. Another component (smaller than S) is present at +0.15eV BE, and might be due to contribution from subsurface silicon atoms, as on the clean surface, and/or to surface orinterface defects. On the Si 2p core-level taken in bulk sensitive mode, we found a very narrow bulk component with atotal full width half maximum (FWHM) of 160 meV at T=120K indicative of an unreacted Si Pb interface on top ofan ideal Si bulk termination. The Pb 5d core-level spectrum is well represented by one doublet, thus suggesting that eachPb atom is adsorbed in a unique environment, i.e., there is no multisite adsorption.