Graphene Thickness Control via Gas-Phase Dynamics in Chemical Vapor Deposition

Graphene has attracted intense research interest due to its exotic properties and potential applications. Chemical vapor deposition (CVD) on Cu foils has shown great promises for macroscopic growth of high-quality graphene. By delicate design and control of the CVD conditions, here we demonstrate that a nonequilibrium steady state can be achieved in the gas phase along the CVD tube, that is, the active species from methane cracking increase in quantity, which results in a thickness increase continually for graphene grown independently at different positions downstream. In contrast, uniform monolayer graphene is achieved everywhere if Cu foils are distributed simultaneously with equal distance in the tube, which is attributed to the tremendous density shrink of the active species in the gas phase due to the sink effect of the Cu substrates. Our results suggest that the gas-phase reactions and dynamics are critical for the CVD growth of graphene and further demonstrate that the graphene thickness from the CVD growth can be fine-tuned by controlling the gas-phase dynamics. A similar strategy is expected to be feasible to control the growth of other nanostructures from gas phases as well.