First-Principles Study Of Electronic Structure Modulations In Novel Layered Transition Metal Dichalcogenides

Layered transition metal dichalcogenides（TMDs）have various crystal structures and rich physical properties according to the different composition elements,which have become a hot research topic in recent years.In order to effectively expand the properties of TMDs and broaden its application prospects,a variety of regulation methods including strain,electric field,adsorption and so on have been widely used.Ternary TMDs can be realized by replacing atoms in MX₂ structure.Janus TMDs can be constructed by replacing the whole layer of chalcogen element atomic layer in MX₂ structure,which effectively breaks the mirror symmetry of traditional monolayer TMDs and introduces the dipole moment in the system.By replacing TMDs of the whole layer in the MX₂ structure,TMDs of different components can be constructed as vertical heterostructures,which can effectively break the spatial inversion symmetry of traditional bilayer TMDs and introduce rich interlayer interfaces into the system.Therefore,while fully studying the particular intra-and interlayer properties of novel layered TMDs such as Janus TMDs and TMDs-based vertical heterostructures,this paper also attempts to study whether various means can effectively regulate the structures and properties of these novel layered systems and explore the physical nature of the regulatory effects.The following research results and conclusions are obtained,which provide theoretical basis for explaining the experimental phenomena related to TMDs and guiding the preparation,design and control of electronic devices based on TMDs.The main innovative results are as follows:1.The semiconductor to metal transformation is realized by replacing metal atoms M in monolayer,bilayer and trilayer semiconductor MX₂ structures.The critical concentration of doping atoms in monolayer,bilayer,and trilayer MX₂ structures is obtained successfully by adjusting the doping concentration.It is possible to realize its application in adjustable alloy structure.2.The Janus monolayer MXY structure is obtained by replacing the X atom layer of monolayer MX₂ with different chalcogen element Y,which exhibits semiconducting characteristics.Both tensile and compressive biaxial strains can reduce the band gap of the system and eventually lead to the transformation of the system into a metal.The Janus bilayer TMDs structure is realized by replacing different positions and layers X with Y in bilayer MX₂,which is a semiconductor and band offset can occur in the system.Among them,SMoS/SeMoS has the maximum band offset.Both electric field and biaxial strain can effectively regulate the electronic structure of the bilayer Janus TMDs system.These results provide a possibility for the realization of tunable optoelectronics and nano electronic devices.3.By replacing the entire monolayer in TMDs,for instance,semiconducting WS₂ and metallic Nb Se₂ are constructed as vertical heterostructure systems with good metallic electrical conductivity.At the same time,the system can achieve effective adsorption,storage and fast migration of external atoms outside and inserting the heterostructure.The absorption of transition metal atoms in the vertical heterostructure constructed by semiconductor MoS₂ and Janus MoSSe structure can effectively introduce magnetism.The resulting spin injection breaks valley degeneracy and realizes valley polarization at valence band maximum of MoS₂/MoSSe under the interaction of exchange field and spin orbit coupling.It is possible to realize the application of electrode material,spin electrics and valley electrics.