Preparation Of Monolayer Tungsten Disulfide And First-principle Study On Its Structures

As a typical transition metal disulfides（TMDs）material,monolayer tungsten disulfide（WS₂）has an excellent electrical and optical properties,and has a wide application prospect in many fields,such as optoelectronic devices,nano-electromechanical systems and so on.The study on the preparation process and modification properties of monolayer WS₂ is of great significance for its application in the future.In this thesis,the process of preparing monolayer WS₂ by chemical vapor deposition（CVD）method is introduced,and the prepared monolayer WS₂ samples are characterized and analyzed.Then,the influence of oxygen doping on the structure and electronic properties of pure and defective monolayer WS₂materials is studied by first principle calculation method.The main work of this thesis is as follows:（1）The crystal structure,properties and applications of WS₂ materials are briefly introduced,and the common preparation techniques of monolayer WS₂ and their research status of modification properties are summarized and analyzed in detail.（2）The basic principle and characteristics of common preparation methods of monolayer WS₂ are briefly introduced.The experimental equipment,raw materials and process for the preparation of monolayer WS₂ by CVD method are also introduced in detail in this thesis,and the prepared monolayer WS₂ samples were characterized and analyzed.（3）The basis thinking of the first principles calculation method is briefly introduced.The development process and basic theoretical framework of density functional theory are also introduced in detail.At the same time,the simulation software used in this thesis is briefly introduced.（4）The changes of structure and electronic properties of oxygen doped the pure monolayer WS₂ are calculated and analyzed based on the first principle method.The results show that with the decrease of oxygen doping concentration,the band gap of monolayer WS₂ increases first and then decreases,and the type of band gap alternates between direct and indirect band gap.（5）The structure and electronic properties of oxygen doped defects monolayer WS₂ are studied based on the first principle method.The results show that oxygen doping can adjust the band gap of defect monolayer WS₂ to some extent.In this thesis,the preparation techniques of monolayer WS₂ by CVD method and their studies of modification properties are studied,and it provides a good experimental and theoretical basis for further application in the field of optoelectronic devices and nanomechanical systems.