Graphene Growth on Different Substrates by Using Chemical Vapor Deposition
The main focus of this thesis is on the fabrications of graphene films on Cu foils and directly on sapphire substrates by using chemical vapor deposition (CVD). The formation mechanisms and the characteristics of the graphene films are investigated. The device performances of the back-gated graphene transistors are also investigated in this thesis. For the graphene films grown on Cu foil, by changing the methane gas partial pressure, the graphene growth rate can be controlled. By increase the pre-growth annealing time, the graphene flake density is rapidly reduced. By transferring the films to SiO2/Si substrates, micro Raman measurements are performed on the graphene films to verify their crystalline qualities. It is observed that the graphene transistor performances are highly dependent on the sizes of the graphene flakes. For the graphene films grown on sapphire substrates, high-quality and large-area films are obtained on sapphire substrates without the assistance of metal catalyst. The graphene film characteristics are investigated by AFM, SEM, TEM, XPS etc. By changing the hydrogen gas flow rate and growth time, the graphene film quality can be greatly improved. The metal catalyst-free growth of graphene film on sapphire substrates has the advantage of application without the necessity of using a metal substrate as a catalyst and the following metal removal process. Because the graphene films prepared by using this method are very smooth on the surface, the development of this growth approach can be very advantageous for the practical applications of the 2-D materials.