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

Abstract

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 gasphase dynamics. A similar strategy is expected to be feasible to control the growth of other nanostructures from gas phases as well.

Gas-phase dynamics in graphene growth by chemical vapour deposition

“…17 As a test, we have also performed simulations using the same pressure of 2666 Pa. 17 As a test, we have also performed simulations using the same pressure of 2666 Pa.…”

“…The heating zone is set after 36 cm from the reactor entrance and 43 cm long. 17 The pressure was fixed at 2666 Pa.…”

“…17 In that experiment, it is found that graphene grown at downstream positions becomes thicker than that at upstream positions. 17 In that experiment, it is found that graphene grown at downstream positions becomes thicker than that at upstream positions.…”

Synthesis of Graphene Films on Copper Foils by Chemical Vapor Deposition

“…[20] The role of the gas-phase reaction may be neglected when the methane partial pressure is low or the gas residence time of the gas flow in the CVD chamber is short, but will become considerable with increasing methane partial pressure or residence time. [16,21] Gas-phase reaction is likely to provide more C-containing species that are active for graphene growth and may break the selflimited process by depositing adlayers on top of the first grown graphene layer. [7,16] For graphene nucleation, both theoretical studies and experimental results show that minimizing both the C supply and a high temperature will lead to a lower nucleation density, as shown in Figure 3a-d. [8,22] Cu surface conditions also affect the graphene nucleation density -a smooth surface with few impurities results in a low nucleation density.…”

Direct synthesis of dimethyl ether on the admixed nanocatalystsof CuO–ZnO–Al2O3 and HNO3-modified clinoptilolite at high pressures: Surface properties and catalytic performance

“…Indirect pathway which is through conventional methanol dehydration [12]. Recently, direct DME synthesis in a single step, which has been attracted significant attention due to elimination of the equilibrium limitation of methanol synthesis reaction [13][14][15]. In the recent method, DME is directly synthesized on a bifunctional catalyst.…”