AB-Stacked Multilayer Graphene Synthesized <italic>via</italic> Chemical Vapor Deposition: A Characterization by Hot Carrier Transport

T he synthesis of graphene on copper foils by chemical vapor deposition (CVD) has attracted considerable attention because of its potential in practical applications. 6 The quality of CVD graphene has yet to match that of the graphene mechanically exfoliated from pristine graphite, and therefore, the CVD growth techniques are still under very active research. Various thermodynamic conditions involving both low pressure and ambient pressure are being addressed. In ref 9, the role of diffusion kinetics was discussed, and it was pointed out that at low pressure the synthesis process is selflimited with respect to the methane (which serves as the carbon source) flow rate, as opposed to the ambient pressure case. At ambient pressure, the mass transport of the carbon species to the catalyst surface dominates the synthesis process and produces multilayer graphene. However, for multilayer graphene, the CVD method usually leads to a turbostratic stacking order (i.e., the layers are randomly oriented with respect to one another). To our knowledge, there has been no report on the CVD synthesis of continuousmultilayer graphene films with AB-stacking order. Recently, bilayer graphene with AB stacking has been achieved by CVD with low hydrogen flow rate or no hydrogen, and reduced hydrogen concentration has also led to the improvement of the quality of CVD graphene. It has been further realized that the absence of hydrogen can change the chemical kinetics of the decomposition of methane into active carbon and hydrogen. Therefore, the hydrogen concentrationmay play a role in determining the active carbon species at different stages of growth and hence may affect the growth rate, the quality, and the stacking order of multilayer graphene. Here, the synthesis of AB-stacked multilayer graphene on Cu foils through ambient pressure CVD is demonstrated. We have achieved continuous multilayer graphene films with AB stacking by using a high methane flow rate and eliminating the hydrogen during the growth. This finding is important not only by shedding light on the CVD synthesis mechanism but also for offering controlled production of multilayer graphene with AB stacking by CVD. The multilayer graphene is further used to fabricate suspended multilayer graphene devices suitable for transport measurements. Hot electron transport is investigated through * Address correspondence to [email protected].