Bernal (AB)-stacked bilayer graphene (BLG) is a semiconductor whose bandgap can be tuned by a transverse electric field, making it a unique material for a number of electronic and photonic devices1,2,3. A scalable approach to synthesize high-quality BLG is therefore critical, which requires minimal crystalline defects in both graphene layers4,5 and maximal area of Bernal stacking, which is necessary for bandgap tunability6. Here we demonstrate that in an oxygen-activated chemical vapour deposition (CVD) process, half-millimetre size, Bernal-stacked BLG single crystals can be synthesized on Cu. Besides the traditional ‘surface-limited’ growth mechanism for SLG (1st layer), we discovered new microscopic steps governing the growth of the 2nd graphene layer below the 1st layer as the diffusion of carbon atoms through the Cu bulk after complete dehydrogenation of hydrocarbon molecules on the Cu surface, which does not occur in the absence of oxygen. Moreover, we found that the efficient diffusion of the carbon atoms present at the interface between Cu and the 1st graphene layer further facilitates growth of large domains of the 2nd layer. The CVD BLG has superior electrical quality, with a device on/off ratio greater than 104, and a tunable bandgap up to ∼100 meV at a displacement field of 0.9 V nm−1.
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We thank J. B. Goodenough, Z. Zhang, N. C. Bartelt, F. Wang, D. Su, E. Stach, G. A. López, E. J. Mittemeijer, L. Ju, and J. Yin for valuable discussions and/or technical assistance. We thank K. Watanabe and T. Taniguchi for providing h-BN crystals. Work at Columbia University was supported by Office of Naval Research (ONR) -N000141310662 and the Nanoelectronics Research Initiative (NRI) through the Institute for Nanoelectronics Discovery and Exploration (INDEX). Work at Austin was supported by the NRI through the South West Academy of Nanoelectronics (SWAN). Work at Sandia was supported by the Office of Basic Energy Sciences, Division of Materials and Engineering Sciences, US Department of Energy (DOE) under Contract No. DE-AC04-94AL85000. Work at Rice University was supported by the ONR and NSF's Chemical, Bioengineering, Environmental, and Transport Systems Division. Work at NREL was supported by DOE under Contract No. DE-AC36-08GO28308, and used the NREL Peregrine Supercomputer and NERSC clusters (supported by DOE DE-AC02-05CH11231). Work at Hong Kong was supported by Hong Kong University of Science and Technology under award RPC11EG39. Work at Harvard University was supported by the Air Force Office of Scientific Research under contract no. FA9550-13-1-0211. Work at Sungkyunkwan University was supported by the convergence technology development program for bionic arm (no. 2014M3C1B2048175) and the Basic Science Research Program (NRF-2014R1A1A1004818) through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning. H. C. was supported by NSF DMR-1122603 and by ONR-N00014-14-1-0330. C. T. was supported by a National Defense Science and Engineering Graduate (NDSEG) Fellowship - FA9550-11-C-0028. R.S.R. was supported by IBS-R019-D1.
The authors declare no competing financial interests.
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Hao, Y., Wang, L., Liu, Y. et al. Oxygen-activated growth and bandgap tunability of large single-crystal bilayer graphene. Nature Nanotech 11, 426–431 (2016). https://doi.org/10.1038/nnano.2015.322
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