Graphene has great and unique physical, chemical and electrical properties, attracting manyresearch interests from different fields all over the world, such assynthesis, transfer and application. Although graphene now just need a small step to its mass-production, this distancestill seems to be along way to finish. Nowadays, the methods researchers use to prepare graphene in labshave problems in the samples such as small-size, defective, non-uniform, etc. In recent years chemical vapor deposition (CVD) has become the most frequently used method to prepare large-scale graphene films, however, problems remain in this method to obtain high quality samples.In this thesiswe first study the change and difference in size, morphology and nucleation ofmillimeter-sized single-crystal graphene grown under different parameters inside and outside a copper envelope. We discuss the possible growth mechanism based on the observation results. We further developed a "two-step" method to grow high-quality single-crystal graphene, and obtain graphene withgrain size as 0.68mm in average,50% increase compared with the "one-step" method, and its adlayer area is about 0.19 n m when the normal method is 0.32 μm, making the average coverage ofadlayers significantly reduced to 0.25%. This new method provesitsadvantages of growing largersize graphene grains with extremely low adlayer coverage. Finally, we also develop a new method to grow high quality polycrystalline graphene films, by adjusting the CVD parameters to not only enable the graphene grain size to millimeter scale but also form a continuous film. We believe the CVD methods we developed in this thesis will open a new way to more graphene applications. |