Synthesis of high-quality graphene with a pre-determined number of layers

A simple and effective strategy is proposed to tune the number of graphene layers by selecting suitable starting graphite, using a chemical exfoliation method. It is found that both the lateral size and the crystallinity of the starting graphite play important roles in the number of graphene layers obtained. Using artificial graphite, flake graphite powder, Kish graphite, and natural flake graphite as starting materials, ∼80% of the final products are single-layer, single- and double-layer, double- and triple-layer, and few-layer (4–10 layers) graphene, respectively, while a mixture of few-layer (4–10 layers) and thick graphene (>10 layers) is obtained when highly-oriented pyrolytic graphite is used. The smaller the lateral size and the lower the crystallinity of the starting graphite, the fewer the number of graphene layers obtained. Moreover, the graphenes obtained are of high-quality with an electrical conductivity of ∼1 × 103 S/cm. These findings open up the possibility for controlled production of high-quality graphene with a selected number of layers in a large quantity.