▎ 摘　　要

We demonstrate that homogeneous single-layer graphene can be grown by simply annealing crystalline Cu(111)/c-plane sapphire (alpha-Al(2)O(3)) at 900 and 1000 degrees C without additional carbon supply. The resulting graphene film shows a high carrier mobility of 1210 cm(2) V(-1) s(-1). However, the annealing at a lower temperature of 800 degrees C gives an amorphous carbon film. Further investigations indicate that graphitization of amorphous carbon and/or adsorbed carbon atoms during chemical vapour deposition (CVD) is not simply a consequence of carbon supersaturation, it is also affected by CVD temperature, and crystallographic plane of the underlying metal, which are essentially correlated to the energy barrier of nucleation. Our results provide the direct experimental evidence to elucidate the influencing factors of graphitization of amorphous carbon, and contribute fundamental insight into the nucleation and growth of graphene to improve its quality for applications.