Honeycomb germanene flakes on Ag nano-islands

Since germanene cannot be exfoliated from a bulk material, and since Ge-based surface alloys are more stable than pure Ge monolayers (MLs) on metal surfaces, the synthesis of germanene flakes remains challenging. Here we report on the synthesis of germanene nanoflakes on Ag ML islands grown on Ag(111). The maximum achievable size is of the order of 30 nm, and germanene growth occurs due to the heavily oversaturated chemical potential for the Ge atoms confined on top of the Ag islands during growth. The nucleation of three-dimensional clusters, however, prevents the formation of larger germanene flakes.