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The Deformation of Wrinkled Graphene Zheling Li, Ian A. Kinloch, Robert J Young, Konstantin S. Novoselov, George Anagnostopoulos, John Parthenios, Costas Galiotis, Konstantinos Papagelis, Ching-Yu Lu, and Liam Britnell ACS Nano, Just Accepted Manuscript • Publication Date (Web): 12 Mar 2015 Downloaded from http://pubs.acs.org on March 13, 2015
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The Deformation of Wrinkled Graphene Zheling Li1, Ian A. Kinloch1, Robert J. Young1*, Kostya S. Novoselov2, George Anagnostopoulos3, John Parthenios3, Costas Galiotis3,4, Konstantinos Papagelis3,5, Ching-Yu Lu6, Liam Britnell6 1
School of Materials and 2School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
3
Institute of Chemical Engineering Sciences, Foundation for Research and Technology – Hellas (FORTH/ ICE-HT), P.O. Box 1414, Patras 26504, Greece, 4
Department of Chemical Engineering and 5Department of Materials Science, University of Patras, Patras 26504, Greece 6
BGT Materials Ltd, Photon Science Institute, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
KEYWORDS: CVD graphene, wrinkles, deformation mechanics, Raman spectroscopy
ABSTRACT
The deformation of monolayer graphene, produced by chemical vapor deposition (CVD), on a polyester film substrate has been investigated through the use of Raman spectroscopy. It has been found that the microstructure of the CVD graphene consists of a hexagonal array of islands
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of flat monolayer graphene separated by wrinkled material. During deformation, it was found that the rate of shift of the Raman 2D band wavenumber per unit strain was less than 25% of that of flat flakes of mechanically-exfoliated graphene, whereas the rate of band broadening per unit strain was about 75% of that of the exfoliated material. This unusual deformation behavior has been modeled in terms of mechanically-isolated graphene islands separated by the graphene wrinkles, with the strain distribution in each graphene island determined using shear lag analysis. The effect of the size and position of the Raman laser beam spot has also been incorporated in the model. The predictions fit well with the behavior observed experimentally for the Raman band shifts and broadening of the wrinkled CVD graphene. The effect of wrinkles upon the efficiency of graphene to reinforce nanocomposites is also discussed.
Following its first isolation in 2004, graphene has shown huge potential in both fundamental studies1 and industrial applications.2 Currently one of the urgent targets is to grow large size, continuous and defect-free graphene. The chemical vapor deposition method (CVD) opens a route to achieve these targets at low cost.3 However, the grain boundaries formed after the graphene grains become stitched together4 affect its performance,5-7 for example, in applications such as transparent electrodes since these boundaries impede electrical transport.4, 8 Moreover, CVD grown graphene typically has to be transferred to other substrates for use,9, 10 during which wrinkles can be induced10, 11 as a result of the different thermal expansion of the substrates,12, 13 the replication of the substrate topography,14 and the transfer process itself.9 These wrinkles have been observed on graphene-based transparent electrodes,15, 16 and are thought to further alter its mechanical stretchability,17 electronic structure,18 and also local potential.19 It is also thought that the presence of wrinkles can affect the deformation of graphene in shear,20 the deformation of graphene oxide paper21 and the ability of graphene oxide to reinforce polymer matrices in
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nanocomposites.22 Although wrinkling appears to be an inherent property of graphene due to its extremely low bending rigidity23 even when it is fully embedded into polymer matrices,24 there has as yet been no systematic experimental study of its effect upon the mechanical response of graphene. Raman spectroscopy is a versatile tool to study graphene,25-27 in particular, it can be useful in the study of number of layers,25, 28 stacking order28, 29 and doping etc.30, 31 It has also been used to monitor the deformation of graphene,32 and to demonstrate that continuum mechanics is still valid even for a one-atom thick material.24,
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In many of the previous studies on large flat
graphene flakes, it was possible to assume uniformity of the graphene within the spatial resolution of the Raman laser spot (around 1-2 µm in diameter). However, when the graphene is
