The Oretical Study Of Strainregulated Electronic Structure And Optical Properties Of Two-dimensional Transition Metal Disulfides

In the past two decades,graphene and graphene-like two-dimensional materials have become a leading research hotspot in the field of physics,chemistry and material science due to their low-dimensionality and high-performance features.Two-dimensional transition metal disulfides（TMDs）have attracted a lot of attention due to the variety of their constituent elements as well as their structural diversity.Two-dimensional transition metal disulfides（TMDs）have a chemical structure in the form of MX₂ and can form pincer or sandwich-type compound structures with multiple atomic layers,mostly with semiconductor properties,and their electronic structure properties can be modulated by strain,which have great prospects for applications in the fields of optoelectronic devices,photoelectric catalysis,and sensors.In this thesis,three types of two-dimensional materials:new Pmmn-ZrS₂ monolayers,2H-CrS₂ monolayers and Cr ZrS₄ monolayers formed by a 1:1 ratio of transition metal atoms（Zr atom and Cr atom）in these monolayers have been systematically investigated using first-principles approach based on density functional theory.The electronic structure properties,mechanistic properties,light absorption properties,carrier mobility and the possibility of these three systems as catalysts for photocatalytic hydrolysis were investigated.The theoretical results of this thesis are of some theoretical reference value for the theoretical and experimental work on photovoltaic devices and photocatalytic hydrolysis catalyst.The specific research contents and conclusions are as follows.1.The electronic structure properties,mechanistic properties,carrier mobility,light absorption properties and photocatalytic hydrolysis properties of the new Pmmn-ZrS₂monolayers were investigated.The results show that（1）Strain can effectively modulate the energy bandgap of Pmmn-ZrS₂ monolayers.Under the strain of-6%to+8%,the Pmmn-ZrS₂energy band gap shows a variation pattern from narrow to wide.（2）The Young’s modulus values of the Pmmn-ZrS₂ system without strain were 83.63（N/m）and 63.61（N/m）along the x-axis and y-axis stretching directions,respectively.Single layer ZrS₂ has anisotropic Young’s modulus and Poisson’s ratio under different strains（-6%-8%）.With the increase of strain（-6%-8%）,the values of Young’s modulus and Poisson’s ratio in different directions increase.（3）The electron mobility of the Pmmn-ZrS₂ monolayer could reach 1.32×10³ cm²V^-1s^-1,and its light absorption coefficient in the UV spectral region could reach 2.5×10⁵ cm^-1.（4）The band gap of monolayer Pmmn-ZrS₂ exceeds 1.23 e V through strain modulation,and the energy band edge position is more suitable to meet the potential requirement of photocatalytic hydrolysis both in pH=0 and pH=7environments.The results show that the electronic structure and optical properties of the new Pmmn-ZrS₂ monolayer structure depend on the strain regulation,and it has broad application prospects in the fields of optoelectronic devices and photocatalytic hydrolysis.2.The electronic structure properties,mechanical properties,carrier mobility,light absorption properties,strain response and photocatalytic hydrolysis properties of the monolayer 2H-CrS₂ structure were systematically investigated.The results show that（1）The energy band structure of the monolayer 2H-CrS₂ structure exhibits good strain modifiability.Under strain modulation,the energy band of the monolayer 2H-CrS₂ system shifts from direct band gap to indirect band gap.The energy band gap values were reduced from 1.82 e V（HSE06）to 1.10 e V（HSE06）under-6%-8%biaxial strain modulation.（2）The Young’s modulus values of the monolayer CrS₂ system without strain were 109.54（N/m）and 89.65（N/m）along the x-axis and y-axis tensile directions,respectively,which were larger than those of the monolayer Pmmn-ZrS₂ system.Under different strains（-6%-8%）,the changes of Young’s modulus and Poisson’s ratio in different directions show anisotropy.（3）Compared with the monolayer Pmmn-ZrS₂ system,this material has a higher light absorption coefficient in the visible region.（4）In addition,the two-dimensional material is able to meet the potential requirement of photocatalytic hydrolysis both in pH=0 and pH=7 environments through strain modulation.3.The structural stability,electronic structure properties,mechanistic properties,carrier mobility,and light absorption coefficient of the monolayer Cr ZrS₄ structure under strain modulation were systematically investigated.And the possibility of the system as a photocatalytic hydrolysis catalyst was demonstrated.The results show that（1）The stability of the monolayer Cr ZrS₄ structure is confirmed by phonon spectroscopy calculations.（2）The monolayer Cr ZrS₄ energy band structure is an indirect band gap.The energy band gap values（1.26 e V（HSE06））are smaller than those of the monolayer ZrS₂（1.46 e V（HSE06））and monolayer CrS₂（1.36 e V（HSE06））systems in the absence of strain.Under strain,the variation law of Young’s modulus and Poisson’s ratio of single-layer Cr ZrS₄ in all directions is similar to that of single-layer ZrS₂.（3）The Young’s modulus values are the smallest（along the x-axis:56.39（N/m）;along the y-axis:43.74（N/m））compared with monolayer ZrS₂ and monolayer CrS₂,indicating that the system has good flexibility.（4）The carrier mobility of the material is lower than that of monolayer ZrS₂ and monolayer CrS₂.However,the material has a good light absorption coefficient in the visible region,which can be achieved 1.6×10⁵cm^-1.（5）By strain regulation,the structure can meet the requirement of photocatalytic hydrolysis in the pH=7environment.