Controllable Growth And Performance Study Of Two Tungsten Disulfide Two-dimensional Atomic Crystals

Becauseof excellent mechanical,electrical and optical properties,two-dimensional materials are widely concerned in the field of materials science.As the important member of the two-dimensional material,transition metal sulfur compounds,such as MoS₂,MoSe₂,WS₂,WSe₂,MoTe₂,WTe₂ and so on,also have many peculiar physical properties.The researches showthat transition metal sulfur compounds have great potential applicationsin the fields of transistors,photodetectors,photovoltaic cells and so on.It is an ideal material for the next generation of electronics and optoelectronics.At present,the main methods of preparation are micromechanical stripping,chemical stripping,chemical vapor deposition,hydrothermal synthesis,etc.The suitable preparation methods and processes are selected to realize the large area and high quality control of the 2-D transition metal sulfur compounds,which is very important for large-scale production and application in the future.This paper focuses on the controllable preparation of large size monolayer,multilayer,heterojunction and large area WS₂ thin film by using chemical vapor deposition?CVD?.The effects of growth process and parameters on the size,morphology and crystallization quality of WS₂ thin films were systematically studied.We used optical microscope,Raman spectroscopy?Raman?and AFM to analyze the pictures and data and determine the size,number and PL of the samples.The main contents are as follows:?1?By chemical vapor deposition?CVD?,S powder is used as sulfur source,WO₃powder is tungsten source,Si/SiO₂?300nm?is the growth base,Ar gas is carrier gas,WS₂film with different layers and large area full covered WS₂ film are grown.The results show that:all WS₂ films can grown at 700?¹000?.For monolayer WS₂ films,they exhibit different morphologies and fluorescence characteristics.The change of stress release on single crystal WS₂ was observed by fluorescence microscopy.The maximum monolayer WS₂ size can reach 500?m,and the bilayer can reach 250?m.The monolayer dominated WS₂ continuous thin films can be grown on 1 square centimeter substrates by improving process.The photoelectric response characteristics of single layer and double layer WS₂atomic layer films were also studied.?2?WS₂/MoS₂ doped and heterojunction are prepared by chemical vapor deposition?CVD?,using S powder as sulfur source,WO₃ powder as tungsten source and MoO₃ as molybdenum source.By controlling the growth process,a two-dimensional WS₂-W_xMo_?1-x?S₂-MoS₂ film with the change of doping gradient was prepared,and the change of the gradient is closely related to the concentration of the source.Vertical heterojunction was prepared by changing heating rate.