Controllable and fast synthesis of bilayer graphene by chemical vapor deposition on copper foil using a cold wall reactor

Bilayer graphene is attractive for digital device applications due to the appearance of a bandgap under application of an electrical displacement field. Controllable and fast synthesis of bilayer graphene on copper by chemical vapor deposition is considered a crucial process from the perspective of industrial applications. Here, a systematic investigation of the influence of process parameters on the growth of bilayer graphene by chemical vapor deposition in a low pressure cold wall reactor is presented. In this study, the initial process stages have been of particular interest. We have found that the influence of the hydrogen partial pressure on synthesis is completely the opposite from that found for traditional tubular quartz CVD. H2/CH4 ratio was also found to effectively influence the properties of the synthesized bilayer graphene in terms of its atomic structure, whether it be AB-stacked or mis-oriented. Different pre-treatments of the copper foil, in combination with different annealing processes, were used to investigate the nucleation process with the aim of improving the controllability of the synthesis process. Based on an analysis of the nucleation activity, adsorption-diffusion and gas-phase penetration were employed to illustrate the synthesis mechanism of bilayer graphene on copper foil. After optimization of the synthesis process, large areas, up to 90% of a copper foil, were covered by bilayer graphene within 15 min. The total process time is only 45 min, including temperature ramp-up and cool-down by using a low pressure cold wall CVD reactor.