Rapid Identification of the Layer Number of Large-Area Graphene on Copper

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Chemistry of Materials, ISSN: 0897-4756, Vol: 30, Issue: 6, Page: 2067-2073

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Zhikai Qi; Xudong Zhu; Hongchang Jin; Tiezhu Zhang; Xianghua Kong; Rodney S. Ruoff; Zhenhua Qiao; Hengxing Ji
American Chemical Society (ACS)
Chemistry; Chemical Engineering; Materials Science
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Chemical vapor deposition (CVD) on Cu foils emerged as an important method for preparing high-quality and large-area graphene films for practical applications. However, to date it remains challenging to rapidly identify the structural features, especially the layer numbers, of CVD-graphene directly on Cu substrate. Herein, we report an O-plasma-assisted approach for identifying the coverage, wrinkles, domain size, and layer number of large-area graphene films on Cu foils by optical microscopy. The wrinkles and grain boundaries of five-layer graphene can be observed with a grayscale increment of ∼23.4% per one graphene layer after O-plasma treatment for only 15 s, which allows for checking graphene on Cu foils with a sample size of 17 cm × 20 cm in a few minutes. The Raman spectroscopy and X-ray photoelectron spectroscopy presents a strong layer number dependence of both the plasma induced graphene defects and Cu oxides, which, as indicated by molecular dynamic simulation, is responsible for the improved image contrast as a result of the interaction between O-ions and graphene with different layer numbers. We expect that this O-plasma-assisted method would be applied to meter-scale samples if atmospheric-pressure plasma is used and therefore will be beneficial for the fast evaluation of CVD-graphene in both laboratory and industry.