![]() In fact, interesting studies have already been performed in the superlattices with the involvement of germanium or/and silicon layers recently. Therefore, the stable germanene and silicene are slightly buckled, with one of the two sublattices of the honeycomb lattice being displaced vertically with respect to the other. As a result, in 2D atomic layers of Si and Ge atoms, the bonding is formed by mixed sp 2 and sp 3 hybridization. However, Ge and Si have larger ionic radius, which promotes sp 3 hybridization, while sp 2 hybridization is energetically more favorable for C atoms. The similarity among germanene, silicene, and graphene arises from the fact that Ge, Si, and C belong to the same group in the periodic table of elements, that is, they have similar electronic configurations. Germanene (or silicene), the counterpart of graphene, is predicted to have a geometry with low-buckled honeycomb structure for its most stable structures unlike the planar one of graphene. Systems involving silicene and germanene may also be very important for their possible use in future nanoelectronic devices, since the integration of germanene and silicene into current Si-based nanoelectronics would be more likely favored over graphene, which is vulnerable to perturbations from its supporting substrate, owing to its one-atom thickness. Silicene and germanene are also zero-gap semiconductors with massless fermion charge carriers since their π and π* bands are also linear at the Fermi level. While the research interest in graphene-based superlattices is growing rapidly, people have started to question whether the graphene could be replaced by its close relatives, such as 2D hexagonal crystals of Si and Ge, so called silicene and germanene, respectively. Among those hybrid systems, the superlattices are considered as one of the most promising nanoscale engineered material systems for their possible applications in fields such as high figure of merit thermoelectrics, microelectronics, and optoelectronics. Moreover, the use of 2D materials could be advantageous for a wide range of applications in nanotechnology and memory technology. It has long been known that the thermal, optical, and electrical transport properties of graphene-based hybrids usually exhibit significant deviations from their bulk counterparts, resulting from the combination of controlled variations in the composition and thickness of the layers. In the past decade, the hybrid systems consisting of graphene and various two-dimensional (2D) materials have been studied extensively both experimentally and theoretically. 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. 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. 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. 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. The results are compared with those of graphene/MoS 2 superlattice. 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. Superlattice provides a new approach to enrich the class of materials with novel properties. ![]()
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