Investigation Of Epitaxial Growth Of Heterostructure And Regulation For Band Structure

All the calculations are performed by means of first-principles calculations as implemented in the Vienna Ab Initio Simulation(VASP) based on density-functional theory(DFT) with the projector augmented wave(PAW) method. Generalized gradient approximation(GGA) using the Perdew–Burke–Ernzerhof(PBE) exchange correlation functional is adopted to describe the exchange–correlation interaction. In our work, we investigate the epitaxial growth of heterostructure for two-dimensional nano material of Group-IV, also the electronic and magnetic properties of other low-dimensional materials are explored.Firstly, we study the geometric, energetics and electronic properties of graphene supported on BC3 monolayer. The results show that overall graphene interacts weakly with BC3 monolayer via van der Waals interaction. The energy gap of graphene can be up to ~0.162 eV in graphene/BC3 heterobilayers. We also find that the interlayer spacing and in-plane strain can tune the band gap of heterobilayers effectively. Interestingly, the characteristics of a Dirac cone with a nearly linear band dispersion relationship of graphene can be preserved, accompanied by a small electron effective mass, and thus the higher carrier mobility is still expected.Next, we investigate the energetics and electronic properties of graphene adsorbed on WS2 surface. We find that the graphene can be bound to WS2 monolayer with an interlayer spacing of about 3.9 ? with a binding energy of –21~32 meV per carbon atom dependent on graphene adsorption arrangement, suggesting a weak interaction between graphene and WS2. The nearly linear band dispersion character of graphene can be preserved in system, with a sizable band gap, depending on graphene stacking patterns on WS2 and the distance between graphene and WS2 monolayer. More interestingly, when the interlayer spacing is larger than 3.0 ?, the band gap opening is mainly determined by the distortion of the isolated graphene peeled from WS2 surface, independent on the WS2 substrate. Further analysis demonstrates that the origin of semiconducting properties can be well understood by the variation of on-site energy of graphene induced by WS2 substrate.Opening a sizable band gap in the zero-gap silicene without lowering the carrier mobility is a key issue for its application in nanoelectronics. Based on calculations, we find that the interaction energies are in the range of –0.09~0.3 eV per Si atom, indicating a weak interaction between silicene and ZnS monolayer and the ABZn stacking is the most stable pattern. The band gap of silicene can be effectively tuned ranging from 0.025 to 1.05 eV in silicene and ZnS heterobilayer. An unexpected indirect–direct band gap crossover is also observed in HBLs, dependent on the stacking pattern, interlayer spacing and external strain effects on silicene. Interestingly, the characteristics of Dirac cone with a nearly linear band dispersion relation of silicene can be preserved in the ABS pattern which is a metastable state, accompanied by a small electron effective mass and thus the carrier mobility is expected not to degrade much.Meanwhile, we study the energetics and electronic properties of silicene and MoSe2 heterobilayer. It is found that the silicene is bound to MoSe2 substrate with a binding energy of –0.56 eV per silicon atom, indicating a weak interaction between two layers. The nearly linear band dispersion character of silicene with a sizable band gap is obtained in Si@MoSe2. Remarkably, the band gap and electron effective mass of HBLs can effectively be tuned by interlayer spacing, external electric field, and strain. These findings indicate that Si@MoSe2 HBLs are promising candidates for high-performance silicene-based FET channel operating at room temperature.Then, the adsorption characteristics of alkali, alkali-earth, group III, and 3d transition-metal(TM) adatoms on germanene are studied. We find that the adsorption of alkali or alkali-earth adatoms on germanene has minimal effects on geometry of germanene. The significant charge transfer from alkali adatoms to germanene leads to metallization of germanene, whereas alkaliearth adatom adsorption, whose interaction is a mixture of ionic and covalent, results in semiconducting behavior with the band gap of 17~29 meV. For group III adatoms, they also bind germanene with mixed covalent and ionic bonding character. Adsorption characteristics of the transition metals(TMs) are rather complicated, though all TM adsorptions on germanene exhibit strong covalent bonding with germanene. The main contributions to the strong bonding are from the hybridization between the TM 3d and Ge pz orbitals. Depending on the induced-TM type, the adsorbed systems can exhibit metallic, half-metallic, or semiconducting behavior. Also, the variation trends of the dipole moment and work function with the adsorption energy across the different adatoms are discussed.The effect of the chlorine atoms on electronic and magnetic properties of AlN nanosheets is also studied. We find that both the bare and fully-chlorinated AlN nanosheets demonstrate semiconducting behavior, while the half-chlorination on surface Al sites leads to the semiconductor-ferromagnetism transition. More interestingly, the chlorination on surface Al sites in monolayer and bilayer AlN nanosheets demonstrates the half-metallic ferromagnetic behavior with 100% spin-polarized currents at the Fermi level, suitable for applications in spintronics at the nanoscale.