As the first identified 2-dimentional material, the unique properties of graphene, such as the ultrahigh electron mobility, had attracted lots of researchers in the related fields. However, the lack of large area and high quality graphene limited the application of graphene-based devices. In the past 10 years, a lot of graphene fabrication methods had been developed. Among these methods, CVD was seen as one of the most promising ways for graphene fabrication. CVD graphene is based on the need of large area continuous graphene films. However, the quality of CVD graphene films would be limited by the grain boundaries. The grain boundaries would reduce not only the stiffness of graphene films but also the electron mobility. Hence, how to reduce the effect of grain boundaries in CVD graphene became an important issue in related applications. The growth of graphene single crystals had been considered as a key to improve the quality of CVD graphene.
In this study, we would demonstrate the growth of millimeter sized single crystalline graphene by a furnace CVD system. By visiting the effect of hydrogen to methane ratio and the effect of growth temperature, we found a suitable growth condition for large graphene single crystals. Besides, under the mm-sized graphene single crystals, we also found the growth of smaller few-layered graphene. Hence, we revisited the effect of growth temperature and found the sublimation of copper played an important role in the system. The reason the smaller grains could only appeared under large grains could be attributed to the copper sublimation would remove the smaller grains. The coverage of the large grains could limit the copper sublimation and created an environment for the smaller grains. We hoped this study could provide some idea about the growth mechanism of large area single crystals and multilayered graphene.||en_US|