Atomic origins of the Si 2p surface core-level shifts of the "prototypical" Si(111)root 3x root 3R(30 degrees)-Ag structure

High-resolution core-level spectra from the Si(111)root 3 x root 3R(30 degr ees)-Ag surface considered as a standard in surface science have been obtai ned at 100 K. The sharp Si 2p spectra comprise three asymmetric surface-shi fted components, pointing to a metallic character of the surface. The stron g S1 component due to the Si first layer atoms bonded to the adsorbed Ag at oms is shifted +250 meV to higher binding energy. This challenges the theor etical prediction of a large charge transfer from the Ag atoms to this top Si layer and points to the importance of final-state effects in the interpr etation of the Si 2p spectra.