Theoretical Study And Tuning The Structures And Properties Of Two-Dimensional Materials WX₂,Arsenene,Antimonene,and The VdW Heterostructures Made Of Them

Two-dimensional materials such as graphene,black phosphorus,arsenene,antimonene,or monolayer transition metal dichalcogenides,and so forth,have the potential to be widely used in optoelectronic devices,photo-catalysis,sensors,and other fields because of their unique electronic properties.Compared with the zero bandgap semiconductor graphene,the monolayer transition metal dichalcogenides(TMDs),arsenene and antimonene all have obvious energy gaps and can be applied in many related fields.However,their application in optoelectronics are limited by the inherent bandgaps.Therefore,the thesis systematically investigated the electronic structures of WX2(X=S?Se?Te),arsenene and antimonene by the first-principles approaches.Meantime,we tried to tune the electronic structures of those 2D materials as well as the van der Waals heterostructures made of them by stress and strain,and doping so that they can satisfy the requirements of practical applications.The major progress made during my master's degree studies are listed in the follow.1.We performed a first-principles theoretical study on the structures and properties of WX2(X=S?Se?Te),and vdW heterostructures WS2/WSe2?WS2/WTe2 and WSe2/WTe2 as well.The impact of number of layers on the properties of WX2 and the strains on band gaps of vdW heterostructures have been demonstrated.We found that the properties of WX2 can be accurately described by HSE06+SOC approach.WS2/WSe2?WS2/WTe2 and WSe2/WTe2 heterostructures exhibit type-?band alignments,which facilitate the particle-hole separation.The uniaxial or biaxial strains can tune the band gaps of these vdW heterostructures.Once the strain exceeds 4%,the transition from the semiconductor to the metal takes place.2.The first-principles calculations found that both monolayer arsenene and antimonene,and As/Sb vdW heterostructure possess an indirect bandgap energy band structure,which is verified by the calculated density of state(DOS)and band structures.The calculated phonon spectra revealed that As/Sb heterostructure is very stable.The band structure of As/Sb vdW heterostructure can be tuned by doping O and S atoms on their surfaces.It is found that when O and S atoms are doped on the surface of arsenene,the energy band structure of arsenene can be transformed from indirect bandgaps to direct bandgaps.We hope that those theoretical works could provide some physical insight and guide for the material design on the basis of those 2D materials with high performance for practical applications.