Criteria for the growth of large-area adlayer-free monolayer graphene films by chemical vapor deposition

Homogeneity is important to material applications for good performance of individual devices, for making AB-stacked bilayer graphene in a layer-by-layer stacking order, and from the point of view of industrial production. Among many properties to be controlled, for the case of graphene, the thickness (or layer number) uniformity is the prerequisite. Chemical vapor deposition (CVD) of C precursors on Cu substrates is the most popular method to produce large-area graphene films. To date, precise control on the number of graphene layers as well as the uniformity over a large area is still very challenging. In this work, with a further understanding of the factors affecting adlayer growth, the synthesis of large-area adlayer-free monolayer graphene (MLG) films was achieved up to tens of squared centimeters in area by just using untreated Cu foil and a normal CVD process. We found that keeping equal C precursor concentration on the two sides of the Cu substrate is a criterion in addition to other factors such as the ratio of H:C and the substrate surface morphology for the growth of adlayer-free MLG. This finding is not only of great significance for the industrial production of large-area adlayer-free MLG films but also instructive for the synthesis of homogeneous few-layer graphene. [Display omitted] •Adlayer-free monolayer graphene films up to 4 × 15 cm2 are synthesized by CVD.•Keeping equal C concentration on both sides of Cu foils is crucial to achieve uniform monolayer graphene films.•Equal C concentration on both sides of Cu foils can be achieved by suspending the Cu foils.