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Triggering the Continuous Growth of Graphene toward Millimeter Size Grain

In this report, we demonstrated a simple but efficient strategy to synthesize millimeter-sized graphene single crystal grains by regulating the supply of reactants in chemical vapor deposition process. Polystyrene was used as a carbon source. Pulse heating on the carbon source was utilized to minimize the nucleation density of graphene on copper foil, while the gradual increase in the temperature of carbon source and the flow rate of hydrogen is adapted to drive the continuous growth of graphene grain. As a result, the nucleation density of graphene grain can be controlled as lower as ~100 nuclei/cm2, and the dimension of single crystal grain could grow up to ~1.2 mm. Raman spectroscopy, transmission electron microscopy and electrical transport measurement show that the graphene grains obtained are in high quality. The strategy presented here provides very good controllability and enables the possibility for large graphene single crystals, which is of vital importance for practical applications.