STRUCTURAL AND ELECTRONIC EVOLUTION ON THE GE(111)-AG SURFACE

High-resolution core-level photoelectron spectroscopy has been used to study three different silver induced surface reconstructions on the G e(111) surface. At the lowest coverage a (4 X 4) structure is formed, which displays a similar Ge 3d core-level line shape as the clean c(2 X 8) surface. Details in the spectra are discussed with respect to pos sible models. The Ge(111)-Ag (root 3 X root 3)R30 degrees structure Ge 3d spectrum is dominated by a very strong contribution assigned to th e two topmost Ge layers in a missing top layer structure, similar to t he Si(111)-Ag (root 3 X root 3)R30 degrees surface. A weak bulk peak i s present on the high-binding-energy side of the spectrum, while a thi rd contribution assigned to Ge in phase boundaries is included in the fit on the lower-binding-energy side. A comparison with results obtain ed from the Ge(111)-Au root 3 structure points to substantial differen ces between the two noble-metal-induced root 3 reconstructions on the Ge(111) surface. Finally, after further deposition of silver at room t emperature, the root 3 geometry is locally broken creating a (6 X 6) s tructure and a new surface-related peak emerges on the low-binding-ene rgy side of the Ge 3d spectrum, which was interpreted as being due to Ge atoms floating on top of the outermost surface layer. The valence b and also revealed the existence of small metallic silver islands.