Cobalt containing nano-islands on Ge(111)-c(2 × 8)

► The deposition of Co on Ge(111) results into the formation of (√13 × √13)R13.9° and (2 × 2) reconstructed islands. ► The structural models of both types of Co induced islands are related to the CoGe2 phase. ► Three types of domain boundaries are observed on the (2 × 2) reconstructed islands.