First-principles Study On The Adjustment Of The Structure And Electronic Properties Of Two-dimensional Material Composites By An External Electric Field

In recent years,graphene has attracted the attention of many researchers owing to its excellent physical and chemical properties since it was successfully prepared.Thus,the two-dimensional materials have become a hot research topic.Among them,the study on modify and design graphene-based two-dimensional materials with the non-covalent interaction attracted lots of focuses.In this paper,density functional theory is applied to study the structural and electronic properties of two-dimensional materials?such as graphene,transition-metal dichalcogenides and their composites?,and the effects of applied external electric field for them by using the DMol3 and CASTEP codes in Materials Studio.The research contents mainly include the following aspects:?1?Density functional theory?DFT?was used to study the adsorption behavior of 1-ethyl-3-methylimidazole tetrafluoroborate?[EMIM][BF₄]?on the graphene surface.The changes of structural and electronic properties under the electric field.A vertical external electric field in the range of-0.2 to 0.5 V?^-11 was applied to the adsorption system,and investigated the changes of the electric field on its structure and electronic properties.The calculation results show that the adsorption interaction between the[EMIM][BF₄]and graphene is dominated via the non-covalent force.And,the?-?stacking interaction makes the adsorption structure become more stable.Furthermore,the positive electric field is good for the stability of the composite,and can be controlled the electronic properties.Therefore,the applied electric field is a good way to broaden the application field of graphene-ionic liquids composites.?2?The similar calculation method was used to systematically study the structural and electronic properties of different proportions of MoS₂/WS₂ lateral heterostructure,and compared with the pristine MoS₂ and WS₂ monolayer.The structural and electronic properties under the external electric field in the range of 0 to 1.0 V?^-11 are investigated.The calculation results show that the band gap of the MoS₂/WS₂ lateral heterostructures lie between the pristine MoS₂ and WS₂ monolayer;by applying external electric fields,the band gaps of MoS₂/WS₂ monolayers undergo a direct-indirect transition,and semiconductor-metal transition can be found in WS2.The results provide a useful information and choice to design the novel two-dimensional materials which can be applied in the optoelectronic devices.?3?The same calculation method as the MoS₂/WS₂ monolayers have been performed to explore the structural and electronic properties of the heterobilayers composed of graphene and the?MoS2?X/?WS2?4-X?X=0,1,2,3,4?monolayers.A vertical external electric field in the range of-1.0 to 1.0 V?^-11 was applied to the heterobilayers,and systematically studied the effects of the external electric field on its structure and electronic properties.The weak coupling between the graphene and the?MoS₂?_X/?WS₂?_4-X-X monolayers can induce a tiny band-gap opening of graphene and formation of an n-type Schottky contact at the G-?MoS₂?_X/?WS₂?_4-X-X interface.Moreover,the combination ratio of MoS₂ and WS₂ can control the electronic properties of the graphene-?MoS₂?_X/?WS₂?_4-X-X heterostructures.The external electric fields can also be used effectively to tune the binding energies,charge transfers,and band structures?the types of Schottky and Ohmic contacts?of G-?MoS₂?_X/?WS₂?_4-X-X heterostructures.These findings suggest that G-?MoS₂?_X/?WS₂?_4-X-X heterostructures can serve as high-performance nano-electronic devices.