| Two dimensional material as a new type of nano-material, is thin film material with one or several atomic layers heterostructure thick. As early as in 2004, a monolayer and a few layers of graphene was prepared by Novoselov and his team, and electrical properties of graphene were studied. Then, Two dimensional materials have drawn great attentions in the scientific community, due to their unique structure and excellent performance. Two dimensional materials are considered to have great potential in applications, such as high frequency electrical devices, transparent electrodes, energy storage, biological medicine, and composite materials. However, the large-scale application of two-dimensional material is dependent on the controllable preparation with large area and high quality. Chemical vapor deposition (CVD) method is one of the most widely used material deposition technology in semiconductor industry. Materials prepared by chemical vapor deposition method usually have the advantages of controllable size, uniform thickness and high quality. Therefore, CVD method is very suitable for the preparation 2D materials with a single layer, large size and high quality. This thesis mainly focuses on the controllable preparation of large size, single crystal graphene and molybdenum disulfide by CVD method. Graphene, MoS2 and MoS2/graphene heterostructure were fabricated, and their optical reflection rate on substrates was studied. In the first chapter, we mainly introduced basic properties of two-dimensional materials, progress in the preparation and application of two-dimensional materials, and our research motive.In the second chapter, we introduced our CVD system, materials used in the growth process, and characterization methods. The third chapter to the fifth chapter is the main part of the thesis, and the specific contents are as follows:(1) Graphene was prepared by chemical vapor deposition method and characterized. We mainly studied the effect of the growth process and growth parameters on the size and thickness of graphene, during the growing process. The obtained graphene samples were characterized by optical microscopy, scanning electron microscopy, atomic force microscopy and Raman spectroscopy. We studied the influence of substrate cleaning, annealing, growth temperature and gas concentration (including the concentration of methane and hydrogen) on the growth of graphene. We also prepared bilayer graphene with large area on the copper foil surface. The growth mechanism are analyzed and explained.(2) MoS2 and MoS2/graphene heterostructure were fabricated by CVD method. We studied the CVD method for the preparation of single layer MoS2 as well as MoS2/ graphene heterostructure. The effects of growth temperature, growth time and the concentration of the reaction source on the growth of single layer MoS2 were studied, and single layer MoS2 film with single crystal size above 40μm was obtained. We successfully grew MoS2/graphene heterostructure on the surface of graphene by CVD method. With several characterization methods, we studied the growth mechanism of MoS2/graphene heterostructure, surface morphology and layer thickness. We also studied the effect of sulfuration on the properties of graphene, and the influence of graphene on the photoluminescence properties of MoS2.(3) We calculated the contrast of several two-dimensional materials on SiO2/Si substrates with different thickness of SiO2, under different incident light. According to our calculation results, we can easily identify the layer number of two-dimensional materials by the optical microscopy, and provide a simple and effective method of characterizing the layer number of two-dimensional materials. We calculated the contrast of graphene, boron nitride,2H-MoS2,2H-MoSe2,2H-MoTe2,2H-WSe2, 2H-NbSe2,3R-WS2 and MoS2/graphene heterostructure on SiO2/Si substrates. |
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