Study On Synthesis Of Large Area WS₂ With High Crystalline Quality By Chemical Vapor Deposition

Two-dimensional materials is a promising material which has caught much interest owing to their unique electricaln and optical properties.They have shown broad applications in high speed transistor, transparent conducting electrodes and energy storage. Large area two dimensional materials with high crystalline quality are basis of the study for their properties and applications. Therefore, how to synthesis the high quality two-dimensional materials with controllable domain size is the focus research in this field. However, the research for the growth of WS2 is still at the initial stage, and controllable synthesis of the large scale WS2 is most important research.In this paper, we use the chemical vapor deposition method to synthesis the Large area monolayer WS2 with high crystalline quality. We make the experimental process more simple and reduce the test cost greatly reduced by improving the growth process. We study the effects of different growth parameters on the number of layer, the crystalline quality and the area of the WS2 samples. In the first chapter, we mainly listed properties, progress and application of two-dimensional materials. We also introduced the synthesis method of two-dimensional materials. The second chapter is our research motive and research contents. In the third chapter, we give main introduction our main experiment for CVD synthesis monolayer WS2. The fifth chapter is the experimental summary, the contents are as follows:1. We improved the growth process which the growth process is no longer required for vacuum conditions and introduced a new atmospheric pressure synthesis system. The high quality graphene were prepared by simple single temperature zone tube furnace, which reduce the experimental cost.2.The single large area and high crystalline quality of WS2 were prepared by using chemical vapor deposition method. We modulated the growth parameters, such as growth temperature, dose of the reaction drug, the growth time and the distance between the sulfur source and substrate, then determined the optimum conditions for the synthesis of WS2. The triangular grain size above 200μm which larger than other paper. When the number of WS2 increases, The typical Raman spectrum of the WS2 will be blue shift and red shift respectively. The wave number difference indicates that the sample is a single layer. A peak was presented at around 619nm demonstrat the band gap of monolayer WS2. The strong intensity peak demonstrated the WS2 is high crystalline quality samples. The controlled growth of WS2 was achieved by adjusting the growth time.3.We studied the effects of different growth parameters on the growth of two-dimensional WS2 samples were studied. We change the reaction temperature, growth time and the dose of the reaction drug respectively.It was found that the effect of temperature on the growth process was maximum. The WS2 samples with were characterized by optical microscopy, photoluminescence spectroscopy and Raman spectroscopy.:(1) Different growth temperature will impact on the size, number and crystalline quality of single crystal WS2. The higher temperature will lead to the larger the size and the higher the crystal quality of WS2. When the temperature is greater than 950℃, it will inhibit the growth of WS2.(2) Different growth time mainly affects the size and layer thickness of WS2. The larger length will lead to the larger the size of the grain size.(3) The grain size and crystalline quality of two tungsten sulfide were mainly influenced by different dosage of drugs. The deficiency of sulfur restrain the growth of the WS2, which decrease the crystal quality.