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

A Pb/Si(100)2x1 surface has been studied at T=120K by high resolution core-level spectroscopy using a third generation 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 atoms after Pb adsorption with the formation of Si–Pb bonds and Pb–Pb symmetric dimers. However, this shift is in the opposite site respect to the bulk peak, as compared with Sb/Si(100)2x1, thus suggesting the interplay of final states screening effects and charge transfer in the core-level position. Another component (smaller than S) is present at +0.15 eV BE, and might be due to contribution from subsurface silicon atoms, as on the clean surface, and/or to surface or interface defects. On the Si 2p core-level taken in bulk sensitive mode, we found a very narrow bulk component with a total full width half maximum (FWHM) of 160 meV at T=120K indicative of an unreacted Si–Pb interface on top of an ideal Si bulk termination. The Pb 5d core-level spectrum is well represented by one doublet, thus suggesting that each Pb atom is adsorbed in a unique environment, i.e., there is no multisite adsorption.