Surface and bulk core-level shifts of the Si(111)√3 √3-Ag surface: Evidence for a charged√3 √3layer

Si 2p and Ag 4d photoelectron spectra have been measured for the Si(111){}3 ×{} {}3 -Ag surface at both surface- and bulk-sensitive photon energies. A dramatic shift of the bulk Si 2p component for the {}3 ×{} {}3 surface has been observed and is attributed to the presence of an inherently charged {}3 ×{} {}3 layer. A single component of surface Si 2p levels is found for the {}3 ×{} {}3 surface. Discussion of structural and growth models of the {}3 -Ag surface is made.