Investigation Of Epitaxial Growth And Tunable Electronic Properties For Silicene-based Heterobilayers

All the calculations are performed using the plane-wave basis Vienna Ab initio simulation package known as VASP code. In our work, we investigate the epitaxial growth of heterostructure for two-dimensional silicon-based material, also the Quantum Spin Hall effect of other low-dimensional materials are explored.Firstly, we study the structural and electronic properties of silicene/silicane and silicene/germanene heterobilayers?HBLs? are investigated by using first-principles methods. The results show that the silicene interacts overall with silicane?germanene? with a binding energy of-50^-70 me V per Si?Ge? atom, suggesting a weakly van der Waals interaction between silicene and substrate. A relative large bandgap with a linear band dispersion of HBLs is opened due to the sublattice symmetry broken by the intrinsic interface dipole between silicene and substrate. Remarkably, the band gap of all these HBLs can also be continually tuned modulated by adjusting the interlayer spacing and strain, independent on the stacking arrangements. Silicene is thus expected to be useful for building high-performance FET channel, which would extend its applicability to possible future nanoelectronics.Next, we investigate the structural and electronic properties of germanene/germanane heterostructure?HTS?. The results indicate that the Dirac cone with nearly linear band dispersion of germanene maintains in the band gap of substrate. Remarkably, the band gap opened in these HTSs can be effectively modulated by the external electric field and strain, along with a very low effective masses and high carrier mobilities. These results provide a route to design high-performance FET operating at room temperature in nanodevices.Quantum spin Hall?QSH? insulators feature edge states that topologically protected from backscattering. However, the major obstacles to application for QSH effect are the lack of suitable QSH insulators with a large bulk gap. Based on first-principles calculations, we predict a class of large-gap QSH insulators in ethynyl-derivative functionalized stanene?SnC₂X; X = H, F, Cl, Br, I?, allowing for viable applications at room temperature. Noticeably, the SnC₂ Cl, SnC₂ Br, and SnC₂ I are QSH insulators with a bulk gap of ⁰.2 eV, while the SnC₂ H and SnC₂ F can be transformed into QSH insulator under the tensile strains. A single pair of topologically protected helical edge states is established for the edge of these systems with the Dirac point locating at the bulk gap, and their QSH states are confirmed with topological invariant Z₂ = 1. The films on BN substrate also maintain a nontrivial large-gap QSH effect, which harbors a Dirac cone lying within the band gap. These findings may shed new light in future design and fabrication of large-gap QSH insulators based on two-dimensional honeycomb lattices in spintronics.Finally, we use first-principles calculations to predict a class of large-gap QSH insulators in functionalized TlSb monolayers?TlSbX₂;?X = H, F, Cl, Br, I??, with sizable bulk gaps as large as 0.22⁰.40 eV. The QSH state is identified by Z₂ topological invariant together with helical edge states induced by spin-orbit coupling?SOC?. Noticeably, the inverted band gap in the nontrivial states can be effectively tuned by the electric field and strain. Additionally, these films on BN substrate also maintain a nontrivial QSH state, which harbors a Dirac cone lying within the band gap. These findings may shed new light in future design and fabrication of QSH insulators based on two-dimensional honeycomb lattices in spintronics.