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.