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Layer-tunable graphene has attracted broad interest for its potentials in nanoelectronics applications.[1,2] However,synthesis of layer-tunable graphene by using traditional chemical vapor deposition method still remains a great challenge due to the complex experimental parameters and the carbon precipitation process.Herein,by performing ion implantation into a Ni/Cu bilayer substrate,the number of graphene layers,especially single or double layer,can be controlled precisely by adjusting the carbon ion implant fluence.The proposed approach for the synthesis of layer-tunable graphene offers more flexibility in the experimental conditions.Being a core technology in microelectronics processing,ion implantation can be readily implemented in production lines and is expected to expedite the application of graphene to nanoeleetronics.Figure(A)illustrates the graphene synthesis process.The Ni/Cu bilayer substrate(i.e.,300 nm Ni layer on top of Cu foil)is implanted with 60 keV C ions.The fluences of 4E15 and 8E15 atoms/cm2 are adopted to obtain monolayer and bilayer graphene,respectively.The implanted samples were annealed at 950 ℃ in Ar and H-2.During the annealing,the top Ni layer is gradually transformed into the Cu.Due to Ni has moderate C solubility,whereas the solubility of C in Cu is extremely low.Therefore,the C solubility in the newly formed alloy may decrease substantially as inter-diffusion of Ni and Cu proceeds to form the Cu-Ni alloy.Following the reduced solubility of C in the newly formed Cu-Ni alloy,the implanted C ions are gradually expelled to the surface and transformed into graphene.Ramar,STM and electrical measurement indicate that both monolayer and bilayer graphene films possess excellent crystalline quality,as described in Figure(B)and(C).