Structural and electronic properties of germanene/MoS(2) monolayer and silicene/MoS(2) monolayer superlattices

Superlattice provides a new approach to enrich the class of materials with novel properties. Here, we report the structural and electronic properties of superlattices made with alternate stacking of two-dimensional hexagonal germanene (or silicene) and a MoS(2) monolayer using the first principles approach. The results are compared with those of graphene/MoS(2) superlattice. The distortions of the geometry of germanene, silicene, and MoS(2) layers due to the formation of the superlattices are all relatively small, resulting from the relatively weak interactions between the stacking layers. Our results show that both the germanene/MoS(2) and silicene/MoS(2) superlattices are manifestly metallic, with the linear bands around the Dirac points of the pristine germanene and silicene seem to be preserved. However, small band gaps are opened up at the Dirac points for both the superlattices due to the symmetry breaking in the germanene and silicene layers caused by the introduction of the MoS(2) sheets. Moreover, charge transfer happened mainly within the germanene (or silicene) and the MoS(2) layers (intra-layer transfer), as well as some part of the intermediate regions between the germanene (or silicene) and the MoS(2) layers (inter-layer transfer), suggesting more than just the van der Waals interactions between the stacking sheets in the superlattices.