934 and 3.176 Å) are much larger than 2.240 and 2.130 Å, the sum of the covalent atomic radius of Ge-S and Si-S atoms (the covalent radius is 1.220/1.110 Å for germanium/silicon and 1.020 Å for sulfur), which suggests that the interlayer bonding in the superlattices is not a covalent one. To discuss the relative stabilities of the superlattices, the binding energy between the stacking sheets in the superlattice is defined as , where E supercell is the total energy of the supercell, and and E Ger/Sil are the total energies of a free-standing MoS2 monolayer and an isolated germanene/silicene sheet, respectively. When N = N(Ge/Si) = 32, the number of Ge/Si atoms in the supercell, selleck chemical E b is then the interlayer

binding energy per Ge/Si atom. When N = N(MoS2) = 25, the number of sulfur atoms in the supercell, then, E b is the interlayer binding energy per MoS2. The interlayer binding energies per Ge/Si atom and those per MoS2 are presented in Table 1. is

calculated by using a 5 × 5 unit cell of the MoS2 monolayer, and E Ger/Sil is calculated by using a 4 × 4 unit cell of the germanene/silicene. The binding energies between the stacking layers of the superlattices, calculated by the PBE-D2 method, are both relatively small, i.e., 0.277 eV/Ge and 0.195 eV/Si for the Ger/MoS2 and Sil/MoS2 superlattices, respectively (see Table 1). The small interlayer binding energies suggest weak interactions between the germanene/silicene and the MoS2 layers. The binding energy also suggests that the interlayer interaction in Ger/MoS2 superlattice

is slightly Ilomastat research buy stronger than that in the Sil/MoS2 one. The interlayer 17-DMAG (Alvespimycin) HCl binding energies are 0.354 eV/MoS2 and 0.250 eV/MoS2 for the Ger/MoS2 and Sil/MoS2 superlattices, respectively, both are larger than 0.158 eV/MoS2 in the graphene/MoS2 superlattice [6]. This is an indication that the mixed sp 2-sp 3 hybridization in the buckled germanene and silicene leads to stronger bindings of germanene/silicene with their neighboring MoS2 atomic layers, when compared with the pure planar sp 2 bonding in the graphene/MoS2 superlattice. In addition, the interlayer bindings become stronger and stronger in the superlattices of graphene/MoS2 to silicene/MoS2 and then to germanene/MoS2 monolayer. Figure 2 shows the band structures of various 2D materials, e.g., the bands of flat germanene/silicene compared with low-buckled germanene/silicene. The band structure of flat silicene is similar to that of low-buckled one. In both kinds of silicene, the systems are semimetal with linear bands around the Dirac point at the K point of the Brillouin zone. On the other hand, the band structure of flat germanene is quite different from that of low-buckled one. The flat germanene is metallic, and the Dirac point does not sit at the Fermi level (but above the E F). The band structure of low-buckled germanene, however, is similar to that of the low-buckled silicene.