First-Principles Study On The Mechanical And Electronic Properties Of Monolayer MoS₂ Based On Tensile Strain

In recent years,flexible electronic devices are developing rapidly,and have wide application prospects in information,energy,medical,national defense and other fields.As an ideal flexible electrode material,layered molybdenum disulfide has excellent conductivity,super hardness,and energy gap sensitivity.In addition,the single layer molybdenum disulfide has large energy gap,which can overcome the zero gap defect of graphene.During the use of flexible electronic devices,the material will inevitably be affected by the tensile strain and the applied electric field,and the vacancy defects produced in the preparation process will also affect the mechanical and electrical properties of the materials.However,the influence of the above factors on the mechanical and electrical properties of molybdenum disulfide is not clear,which largely limits its wide application in flexible electronic devices.In this thesis,based on the density functional theory,the first principle of the mechanical and electricity characteristics of single layer molybdenum disulfide under tensile strain conditions is studied.The main contributions of this work are as follows:(1)The basic structure,properties,preparation methods and application prospects of molybdenum disulfide are introduced,and the current research status of mechanical and electronic properties of single layer molybdenum disulfide materials at home and abroad is also described.(2)The theoretical basis of the first principle calculation is introduced,including the density functional and the ab initio theory,and the VASP software used in the calculation process of the first principle is briefly introduced.The configuration scheme of the running file in the calculation process is expounded,and a single layer molybdenum disulfide model with intrinsic and sulfur vacancy defects has been established.(3)The effect of vacancy defects on the mechanical properties of single layer molybdenum disulfide under tensile strain condition was studied.The mechanical parameters such as modulus of elasticity,theoretical strength and Poisson's ratio under given conditions are calculated.Then the nature of the change of mechanical properties is revealed from the angle of charge distribution.Finally,the effect of sulfur vacancy concentration on the mechanical properties is further analyzed.The results show that the lattice distortion is caused by the existence of vacancy defects,which greatly weaken the modulus and strength of molybdenum disulfide.At the same time,the Poisson's ratio shows obvious anisotropy under the strain of tensile strain.(4)The influence of vacancy defects on the electrical properties of single layer molybdenum disulfide under tensile strain condition was studied.The band gap values of single layer molybdenum disulfide under tensile strain,vacancy defect and external electric field are calculated.It is found that the above factors have some control effect on the band gap size and direct indirect band gap switching of single layer molybdenum disulfide.The effects of intrinsic and sulfur vacancy defects on the band structure,density of state,effective mass and charge density of single layer molybdenum disulfide under tensile conditions were also analyzed.The results show that the impurity state energy band introduced by vacancy defect is very sensitive to tensile strain,which is the fundamental reason for the change of electrical properties.Through a large number of first principles calculation and results analysis,the effects of strain and defect on the mechanical and electrical properties of single layer molybdenum disulfide are examined.It provides theoretical support for the preparation and performance control of single layer molybdenum disulfide in flexible electronic devices and other related fields.