Deposition of 1 monolayer (ML) of Ag on the clean Ge(111) surface, followed by annealing at 300°C for 2 min, results in a sharp √3 × √3 low-energy electron diffraction (LEED) pattern. This surface transforms into a √39 × √39 surface, as observed by LEED, due to a tiny amount of additional Ag atoms when the temperature is below approximately -20°C. The presence of the additional Ag leads to an increased filling of two partially occupied surface bands. By depositing approximately 0.2 ML of Ag on the √3 × √3 surface, it transforms into a 6 × 6 periodicity. The addition of Ag leads to an interesting transition from the metallic surfaces (√3 × √3 and √39 × √39) to the semiconducting 6 × 6 surface with a gap of around 0.2 eV with respect to the Fermi-level. On the 6 × 6 phase, the lower one of the partially occupied surface bands of the √3 × √3 and √39 × √39 surfaces seems to be entirely pulled down below the Fermi-level, while the upper one is missing. The electronic structures of the different Ag/Ge(111) surfaces are also discussed in comparison with the Ag/Si(111) surfaces. © 2001 Elsevier Science B.V.
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