Inspired by the fruitful results based on graphene, two dimensional structures of group-IV elements (Si, Ge) are currently the most investigated materials in physics and nano science. Silicene, the silicon analogy of graphene, had already been synthesized experimentally, but the germanium analogy of graphene has not been synthesized experimentally yet. Only a few theoretical works predicted that graphene like 2-D honeycomb structure of germanium is stable with low buckling. We experimentally observed the phase evolutions for germanium growth on Ag(111) by low energy electron diffraction. We observed that the phase evolutions were strongly dependent on the amount of germanium coverage on Ag(111). We obtained a (9√3 × 9√3)R 30° pattern by germanium adsorption on Ag(111) at RT and the pattern become clear after annealing at 415 K. The (9√3 × 9√3)R 30° ppattern is analogous to the (6√3 × 6√3)R 30° ppattern of graphene formation on SiC(0001). We also observed the atomically resolved STM image after one monolayer germanium adsorption on Ag(111). By the observation on the STM image, we observed a honeycomb structure and by further close observation on larger area, we observed the (9√3 × 9√3)R 30° pmoiré structure. On the basis of the LEED and STM results, we have proposed an atomic model for germanene, the germanium analogy of graphene, growth on Ag(111).
Keywords: Ge, Ag(111), germanene, LEED, STM