The Synthesis And Characterization Of Bilayer Graphene And The CdS Clusters/ Graphene Composite

Chemical Vapor Deposition(CVD) growth of graphene has attracted widely attention due to its potential in industrial production of graphene. When using copper as the substrate and catalyst during the CVD growth, large area monplayer graphene is facile to be synthesized on the surface of copper. This method plays a significant role in the development of graphene’s industrial application. Different from monolayer graphene, AB-stacked bilayer graphene has a tunable bandgap opening induced by a vertical electric field, which shows potential application in electronic devices. However, growth of graphene on copper foil by CVD is a self-limiting growth process, which bring challenges to grow uniform bilayer graphene.The composites combining graphene and semiconductor nanoparticles are promising in the application of photoelectric devices. The conventional method to fabricate these composites is by linking reduced oxide graphene (RGO) and semiconductor nanoparticles in solutions. However, the conductivity of RGO is not as good as intrinsic graphene, which lower the efficiency of charge transfer from semiconductor nanoparticles to graphene. To find a new approach of synthesizing semiconductor nanoparticles/graphene composite is important for the development of graphene-based photoelectric devices.In this thesis, we first explored the feasibility to synthesize large area uniform bilayer graphene by atmospheric pressure CVD growth using solid carbon source. Based on that, we then deposited Cadmium sulfide(CdS) nano clusters onto graphene and investigated the property of the CdS clusters/graphene composite. The main results of this thesis are described as follows:1) We synthesized different layer graphene sheet on copper foils by atmospheric pressure CVD using solid carbon source, i.e. polystyrene as the feedstock. After that, we characterized the graphene sheets by Optical Microscope, Raman spectrum, Transmission Electron Microscope(TEM). We further concluded the growth process of the graphene sheets, that is nuclei formation-nuclei growth--erge of single crystal graphene--continuous graphene. During the growth experiments, we found that the atmospheric growth pressure and a high H2 proportion in the mixed carrier gas are effective to break the self-limited process of graphene growth on copper surfaces. Besides, we find that the supply of carbon source, the rate of gas flow are vital for the layer and quality of grown graphene, which laid foundation for the controllable growth of large area bilayer graphene.2) In the condition of an atmospheric growth pressure and a high H2 proportion of carrier gas, we synthesized large area uniform AB-stacked bilayer graphene on cooper foils by controlling the temperature of polystyrene. We have examined the bilayer nature of synthesized graphene by Raman spectrum, High Resolution TEM and Atomic Force Microscope(AFM). Furthermore, by the analysis of Selected Area Electron Diffraction(SEAD) and Raman spectrum, we confirmed that the bilayer graphene is in AB stacking order. Statistics data based on Raman mapping show that the bilayer graphene is uniform with a high coverage and good quality. Then we analyzed the reasons and mechanism about the growth of large area bilayer graphene. Atmospheric pressure, solid carbon source and a high H2 proportion in carrier gas all contribute to the bilayer growth by breaking the self-limiting process of graphene growth on copper surfaces. While regulating the liner increase of heating temperature to polystyrene is vital for the uniformity of bilayer graphene.3) Semiconductor CdS nano clusters was prepared by home-made ultrahigh vacuum cluster deposition systems. We investigated on the main parameters which are important for the preparation including the value of sputtering voltage, liquid hydrogen cooling, flux of buffer gases and sputtering gases. Then we fabricated CdS cluster/graphene composite by depositing CdS clusters onto graphene synthesized by CVD. We found an increased electric current of the composite in light, which could attribute to the charge transfer from CdS clusters to graphene.