Since the electronic states around K point are almost fully contributed from the germanene/silicene layers, the gaps that opened for the superlattices are due to the interactions between the germanene/silicene

layers only. In other words, the formation of the small-sized band gaps at the K point is due to the symmetry breaking within the germanene/silicene layers caused by the introduction of the MoS2 selleck compound sheets in the formation of superlattices [43–46]. Figure 2 Band structures of various 2D materials. (a) Flat germanene, (b) flat silicene, LY2603618 purchase (c) graphene, (d) low-buckled germanene, (e) low-buckled silicene, and (f) MoS2 monolayer. Figure 3 Band structures of free-standing. (a) Germanene calculated with a 4 × 4 supercell, (b) MoS2 monolayer calculated with a 5 × 5 supercell, and (c) silicene calculated with a 4 × 4 supercell. (d, e) The band structures of Ger/MoS2 and Sil/MoS2 superlattices, respectively. The contributions from the germanene/silicene and MoS2 layers to the band structures of the superlattices are shown

with blue and green dots, respectively. The detailed band structures in the vicinity of the opened band gap are inserted. Red dashed lines represent the Fermi level. To further explore the bonding nature and the charge transfer in the Ger/MoS2 and Sil/MoS2 superlattices, the contour plots of the charge density differences (∆ρ 1) on the planes passing through germanene, silicene, and sulfur Thiamet G layers (in the x-y plane) are shown in Figure 4a,b,c,d. The deformation charge density ∆ρ 1 is defined as , where represents Selleck INCB28060 the total charge density of the superlattice and is the superposition of

atomic charge densities. The deformation charge density shown in Figure 4a,b,c,d exhibited that the formation of the Ger/MoS2 and Sil/MoS2 superlattices did not distort significantly the charge densities of germanene, silicene, or sulfur layers, when compared with the deformation charge density in the free-standing germanene, silicene layers, or sulfur layers in the MoS2 sheets (not shown). Figure 4e,f shows the contour plots of ∆ρ 1 on the planes perpendicular to the atomic layers and passing through Mo-S, Ge-Ge, or Si-Si bonds in the Ger/MoS2 and Sil/MoS2 superlattices. As in the case of isolated germanene/silicene or MoS2 monolayer (not presented), the atomic bonding within each atomic layer in both the superlattices are mainly covalent bonds. Moreover, shown in Figure 4g,h, we also present the charge density differences (∆ρ 2) of the same planes as in Figure 4e,f. The ∆ρ 2 is defined as , where , ρ slab(Ger/Sil), and ρ slab(MoS2) are the charge densities of the superlattice, the germanene/silicene, and the MoS2 slabs, respectively. In the calculation of ρ slab(Ger/Sil) and ρ slab(MoS2), we employ the same supercell that is used for the superlattice.