Electronic structures of Ag/Ge(0 0 1) surfaces

The electronic states of Ag deposited Ge(0 0 1) surfaces at 100 K and their changes after the annealing at room temperature were investigated by using low-temperature angle-resolved photoelectron spectroscopy. Below 1 mono-layer of Ag, the surface did not show any metallic behaviors both at 130 K and after the annealing at room temperature. At 130 K, the Ag atoms adsorb as Ag ad-dimer at valley bridge site between the adjacent substrate dimer rows without breaking the Ge dimer structure. After the annealing at room temperature, the signal from the Ge dimer back-bond is significantly modified indicating changes in the dimer structure. All these findings are consistent with the previous observations by scanning tunneling microscopy: thermal diffusion and clustering of initially adsorbed Ag aggregates below 180 K; transformation of internal structure of Ag islands by further annealing above 240 K. The present study strongly supports the transformation as a restructuring process between Ag and Ge atoms at the interface.