Investigation Of The Design And Tunable Of Quantum Properties For ?-Group Two-dimension Materials

Graphene,is attractive in spintronics devices due to its unique properties of the high carrier mobility and the potential application,which promoted the development of the two-dimensional nano material of Group-? element.On the other hand,the prototypical concept of Quantum Spin Hall insulator is first proposed by Graphenen.In this paper we investigated the electronic property and Quantum Spin Hall effect which were calculated by the first-principle calculations based on density-functional theory.Firstly,we investigated the geometric and electronic properties of silicene/Sc₂CF₂ heterojunction which is formed by the van der Waals interaction.We predict that the Dirac cone of silicenen maintains in the heterojunction with a sizable band gap about 36-48 meV.On the other hand,we calculated the variation of band gap by the interlayer spacing and strain.Interestingly,the nearly linear band dispersion of silicene can be retained in a certain range of the interlayer spacing and strain.These findings are promising for high-performance field effect transistors with high carrier mobilities operating at room temperature in nanoelectronics.Topological insulators?TIs?with the unique quantum spin effect have attracted widespread attention in condensed matter physics.One of the most interesting feature is the quantum spin Hall?QSH?effect in two-dimensional materials,characterized by an insulator bulk-gap and gap less edge states at its boundaries protected by the time-reversal symmetry,which can be applied in novel quantum electronic devices with low energy dissipation.Nevertheless,the tiny QSH band gap obstructed the application and development at room temperature.In order to solve the challenge,we calculated a methyl-functionalized tin film named SnCH3 which is a topological trivial insulator in the equilibrium state by first-principle method.Then we find a transform from normal insulator to topological insulator under the biaxial stress by Z₂ topological invariant and the edge states.Moreover,we find that the BN can be an excellent substrate to epitaxial growth the SnCH3,for which the topological character remain intact.Then,we predicted a like-graphene hexagonal honeycomb Plumbene based on first-principle calculation.Then we found a huge band gap about 1.34 eV in the hydrogenated and halogenated plumbene named PbX?X= H,F,Cl,Br,I?.Meanwhile,the fantastic QSH effect can be retained under the biaxial stress within a reasonable range by calculated the topological invariant Z₂=1.The counter-propagating gapless edge states which completely connect the conduction and valence bands exhibited opposite spin-polarization also were calculated to confirm the topological property of the all structures.Furthermore,a high-dielectric-constant BN is proposed to be an ideal substrate to experimental realization of PbX,maintaining the QSH effect.The discovery of PbX represents a significant advance in the development of TIs.Finally,for purpose of exploring the practical application of the plumbene,we projected a new QSH insulator of cyanogen-decorated plumbene named PbCN.In this work,based on first-principle calculation the result of gapless helical edge states and topological invariant Z₂ indicated that the QSH phase can be existed in the PbCN monolayer.Experimentally,we proposed a nontoxic and environment friendly cyanide reagent such as K4[Fe?CN?6] to be an ideal source of the cyano,which can generate the final products with mixture of halogen and CN groups.Therefore,we calculate the derivative F0.5Pb?CN?0.5 and find that the fascinating QSH state with huge band gap was retained.Furthermore,we also explored a 7-layered rock-salt crystal BaTe as the substrate for PbCN monolayer.In comparison to the pristine PbCN,the band inversion is presented,maintaining the topology.The excellent properties of PbCN can be provided as a promising platform for practical application spintronic devices at high temperature.