Study On The Mechanical And Electrical Properties Of Monolayer Tungsten Disulfide Under Mechanical Strain

Tungsten disulfide(WS₂)is a two-dimensional direct band gap semiconductor material with excellent electrical,optical and mechanical properties and has wide application prospects in flexible electronic and micro-nano-electronic systems.It is inevitable that various defects will be introduced in the preparation of monolayer sulfide layers,which will affect its properties.In this thesis,the mechanical and electrical properties of the intrinsic and monolayer tungsten disulfide containing vacancy defects are studied by the first-principles calculation method.The main research work in this thesis is as follows:(1)The crystal structure and application prospect of monolayer WS₂ were introduced,and the related research status of mechanical and electrical properties of monolayer WS₂ was summarized and analyzed in detail.(2)The first principle method was introduced briefly,the derivation process and basic theoretical framework of density functional theory were expounded,and the relevant simulation software used in this paper was briefly introduced.(3)An orthogonal supercell model of intrinsic monolayer WS₂ was established and its mechanical and electrical properties under tensile strain were calculated and analyzed based on first-principles calculation method.The results show that the Young's modulus and ultimate strength of the intrinsic monolayer WS₂ in the armchair direction are larger than that in the zigzag direction,and Poisson's ratio shows obvious chiral effect indicating that its mechanical properties are anisotropic.In electrical research,strain plays a role in regulating the band gap of the intrinsic monolayer WS₂.The band structure changes from direct band gap to indirect band gap under tensile strain,while band gap decreases monotonously with increasing band gap strain.(4)The monolayer WS₂ model containing two sulfur vacancy defects were established to study its crystal structure and mechanical parameters such as young's modulus,ultimate strength and poisson's ratio under tensile strain.At the same time,the effect of different sulfur vacancy concentration defects on the mechanical properties of monolayer WS₂ was studied.The results show that the introduction of sulfur vacancy causes the lattice shrinkage near the vacancy of monolayer WS₂ cell and reduces its ultimate strength.The mechanical properties of the defect system are still anisotropic,and the increase of sulfur vacancy concentration will greatly weaken its ultimate strength.(5)Several types of point vacancy defects in WS₂ cells were briefly introduced,and the single-layer WS₂ electrical properties containing two sulfur vacancy defects under tensile strain were studied.The results show that the impurity energy level is introduced in the band gap region with vacancy defect monolayer WS₂,which reduces the band gap of the defect system,and the tensile strain changes the structure and band gap size of the band.In this thesis,based on the first-principles calculation method,the mechanical and electrical properties WS₂ single-layer with intrinsic and vacancy-containing defects are studied,and the influence of uniaxial tensile strain on its mechanical and electrical properties is investigated.The work in this thesis provides a good theoretical basis and data support for further research on the application of single-layer WS₂ in strain engineering and flexible electronic devices.