title: Oxygen-activated growth and bandgap tunability of large single-crystal bilayer graphene.
abstract: 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 devices. A scalable approach to synthesize high-quality BLG is therefore critical, which requires minimal crystalline defects in both graphene layers and maximal area of Bernal stacking, which is necessary for bandgap tunability. 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 10(4), and a tunable bandgap up to ∼100 meV at a displacement field of 0.9 V nm(-1).
authors.affiliation: Department of Mechanical Engineering, Columbia University, New York, New York 10027, USA.
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authors.initials: Y
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authors.affiliation: Department of Mechanical Engineering, Columbia University, New York, New York 10027, USA.
authors.forename: Lei
authors.identifier: 0000-0002-1919-9107
authors.initials: L
authors.lastname: Wang
authors.affiliation: Department of Materials Science and NanoEngineering, Rice University, Houston, Texas 77005, USA.|National Renewable Energy Laboratory, Golden, Colorado 80401, USA.
authors.forename: Yuanyue
authors.identifier: 0000-0002-5880-8649
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: Hua
authors.identifier: 0000-0003-0676-3079
authors.initials: H
authors.lastname: Chen
authors.affiliation: Department of Mechanical Engineering and the Materials Science and Engineering Program, The University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: Xiaohan
authors.initials: X
authors.lastname: Wang
authors.affiliation: Department of Mechanical Engineering, Columbia University, New York, New York 10027, USA.
authors.forename: Cheng
authors.initials: C
authors.lastname: Tan
authors.affiliation: Sandia National Laboratories, Livermore, California 94550, USA.
authors.forename: Shu
authors.initials: S
authors.lastname: Nie
authors.affiliation: School of Mechanical Engineering, Sungkyunkwan University, Suwon 440-746, Korea.
authors.forename: Ji Won
authors.initials: JW
authors.lastname: Suk
authors.affiliation: Department of Materials Science and Engineering, University of Central Florida, Orlando, Florida 32816, USA.
authors.forename: Tengfei
authors.initials: T
authors.lastname: Jiang
authors.affiliation: Department of Mechanical and Aerospace Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong 999077, China.
authors.forename: Tengfei
authors.initials: T
authors.lastname: Liang
authors.affiliation: Department of Mechanical Engineering, Columbia University, New York, New York 10027, USA.
authors.forename: Junfeng
authors.identifier: 0000-0002-8057-7429
authors.initials: J
authors.lastname: Xiao
authors.affiliation: Department of Mechanical and Aerospace Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong 999077, China.
authors.forename: Wenjing
authors.initials: W
authors.lastname: Ye
authors.affiliation: Department of Physics, Columbia University, New York, New York 10027, USA.
authors.forename: Cory R
authors.initials: CR
authors.lastname: Dean
authors.affiliation: Department of Materials Science and NanoEngineering, Rice University, Houston, Texas 77005, USA.
authors.forename: Boris I
authors.initials: BI
authors.lastname: Yakobson
authors.affiliation: Sandia National Laboratories, Livermore, California 94550, USA.
authors.forename: Kevin F
authors.initials: KF
authors.lastname: McCarty
authors.affiliation: Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: Philip
authors.initials: P
authors.lastname: Kim
authors.affiliation: Department of Mechanical Engineering, Columbia University, New York, New York 10027, USA.
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authors.initials: J
authors.lastname: Hone
authors.affiliation: Texas Instruments, Dallas, Texas 75243, USA.
authors.forename: Luigi
authors.initials: L
authors.lastname: Colombo
authors.affiliation: Department of Mechanical Engineering and the Materials Science and Engineering Program, The University of Texas at Austin, Austin, Texas 78712, USA.|Center for Multidimensional Carbon Materials, Institute for Basic Science, Ulsan National Institute of Science and Technology, Ulsan 689-798, Korea.
authors.forename: Rodney S
authors.initials: RS
authors.lastname: Ruoff
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