Study On Two Types Of Lateral Heterostructures From First-principles

Since the advent of graphene,its excellent performance has stimulated the enthusiasm of researchers for the research of new 2D materials.Its rapid development involves the fields of solid physics,materials science and engineering.So far,two-dimensional materials that have been discovered or synthesized have been boron nitride,silicene,germanene,stanene;semiconducting transition metal dichalcogenides(TMDCs),such as MoS2,WS2,MoSe2,WSe2;Boron nitride single layer with large band gap.With the in-depth study of two-dimensional materials,and people's increasing demands for the integration and functionality of electronic devices and optoelectronic devices,Among them,the realization of effective control of two-dimensional material heterostructures is a prerequisite for building high-performance,high-integration devices.Therefore,more and more 2D heterostructures are concerned by scientific researchers.With regard to the development of heterogeneous,based on the characteristics of the layered material,we can stack two different single-layered two-dimensional materials layer by layer vertically or combine them together in a plane to form longitudinal heterostructure(van der Waals heterojunction)and lateral heterojunction.The heterogeneity of longitudinal heterostructure has been extensively studied in theory and experiment.In the early stage,it was synthesized by a physical transfer method.Later,as the process was improved,it could be grown directly on the substrate by chemical vapor deposition.However,the lateral heterojunction is different from the traditional van der Waals heterostructure,which can only be derived by chemical vapor deposition method.At present,two representative heterogeneous systems include graphene and hexagonal boron nitride heterojunction and transition metal disulfide heterostructure.The atomic structure and electron band arrangement of the heterojunction interface are the key elements for the development of 2D devices in the future.The synthesis of complex 2D heterostructures is the basis and key issue for their application.In this paper,we based on experimentally successfully prepared lateral heterostructures composed of TMDCs(WS2/WSe2/MoS2)and First-principles based on density functional theory for theoretical analysis and research.The electronic properties of the lateral heterojunction formed by graphene and boron nitride are also controlled.By changing the dimension width,stress and adsorption site,these two kinds of transverse heterostructure are studied respectively,and the potential of application in the future single layer electronic devices is revealed.The following is the main content of this paper:Chapter 1:The development background of two-dimensional materials and the research progress of heterostructure are introduced.Chapter 2:Introduced the basic knowledge of density functional theory(DFT)and the first-principles calculation package used in this paper.Chapter 3:By studying the electronic properties of three different materials in the WS2/WSe2/MoS2 heterostructure.three different lattice parameter WS2/WSe2/MoS2 lateral heterojunctions were constructed.This also means that three kinds of different stress.Through the regulation of stress,we find that the lateral heterostructure of these three different lattice parameters produces different bandgap,and its band gap showed a direct to indirect changes.At the same time,we observe the energy band diagrams and we can see that there are two different energy band alignments,type?and type?.Through the regulation of its lattice size,we find that the band gaps of these three kinds of lateral heterojunctions are gradually decreasing due to the quantum size effect.At the same time,we qualitatively analyzed the electron distribution and transfer at the lateral heterointerface of WS2/WSe2/MoS2.Our results show that the 2d planar heterostructure of WS2/WSe2/MoS2 presents rich and adjustable electron characteristics,and has broad prospects in the application of optical emission and photoelectricity.Chapter 4:By means of density functional theory,the system of lateral heterostructure of different sizes and adsorption sites and their corresponding electronic structures were studied.The results show that all the different lateral heterojunction systems have relatively good planar structures without any structural distortion.By changing the different adsorption sites,the results show that the bandgap opening size is also different,there are different situations of metals,insulators and semiconductors.As the size increases,the band gap presents a decreasing trend.This result helps us to select the structure we need by adjusting the adsorption sites and the size,which is of great significance in photocatalysis.At the same time,in the fully-adsorbed configuration,double Dirac cones have emerged.This novel effect is very much to be studied,making it more suitable for use in electronic devices.Chapter 5:Summarizing the research content of this paper and gives a prospect for the formation of transverse heterogeneity of two-dimensional materials.