We report the synthesis of single-layer graphenes from ethanol using, what we call, “flash cooling” just after chemical vapor deposition. The single-layer graphenes synthesized are high-quality and several micrometers in grain size as revealed by Raman spectroscopy. Detailed comparison of the cooling processes suggests that the single-layer graphene growth does not occur during the carbon precipitation but rather stems from surface diffusions of carbon on a nickel substrate. Because of the present simple and easiness for the large-scale synthesis under an inert gas atmosphere and at atmospheric pressure, the present method can easily be applied for the future large-scale and low-cost graphene production.

The synthesis of graphene and hexagonal boron nitride (hBN) hybrid sheets has been achieved using a two-step chemical vapor deposition (CVD) process. Individual grains of single-layer graphene are grown from methane, and hBN is, then, synthesized from ammonia borane on the same copper (Cu) foil. Optical absorption and Raman measurements reveal that the hBN is formed on the bare surface of Cu foil and the graphene grains play a crucial role as an inactive protective layer of Cu foil for the ammonia borane CVD. Furthermore, the hBN growth is found to be initiated preferentially by the edge of graphene grains.