Title: Hydrogen-modulation method for wafer-scale few-layer single-crystal graphene growth

Single-crystal few-layer graphene films have potential applications in microelectronic and optoelectronic devices. Considerable efforts have been taken to prepare large-area bilayer graphene through chemical vapor deposition, but the growth of uniform graphene films with increased layers remains challenging. Herein, a hydrogen-modulation method for growing wafer-scale few-layer single-crystal graphene through chemical vapor deposition was proposed. By controlling the hydrogen flow rate at different stages, the dissolution amount and segregation process of carbon atoms in a CuNi substrate can be regulated separately. The hydrogen-modulation method fully exploits the effect of the dissolution–segregation mechanism, and the number of graphene layers can be controlled by modulating the hydrogen flow rate. Through the proposed method, the coverages of bilayer and trilayer graphene can reach more than 99% and 95%, respectively. The stacking and uniformity of few-layer graphene were evaluated by Raman and microstructure characterization, and bilayer and trilayer graphene were confirmed as AB and ABA stacks, respectively. Transmission line test structure and field effect transistor were prepared to verify the electrical properties of bilayer graphene. Results show that the square resistance of bilayer graphene is significantly lower than that of single-layer graphene, and it can also achieve high on-state current on field effect transistor.