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 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.
Highlights
Following its first isolation in 2004, graphene has shown huge potential in both fundamental studies[1] and industrial applications.[2]
The scanning electron microscope (SEM) images in Figure 1a of the surface of the chemical vapor deposition method (CVD) graphene/PET show the network of CVD graphene islands separated by wrinkles with a height of around 20 nm, as revealed by atomic force microscopy (AFM) (Figure 1b and d)
It is thought that the wrinkles form in the CVD graphene for at least two reasons
Summary
Following its first isolation in 2004, graphene has shown huge potential in both fundamental studies[1] and industrial applications.[2]. Grown graphene typically has to be transferred to other substrates for use,[9,10] during which wrinkles can be induced[10,11] 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 local potential.[19] It is thought that the presence of wrinkles can affect the deformation of graphene in shear,[20] the deformation of graphene oxide paper,[21] and the ability of graphene oxide to reinforce polymer matrices in nanocomposites.[22] wrinkling appears to be an inherent property of graphene due to its extremely low bending rigidity[23] 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. VOL. 9 ’ NO. 4 ’ 3917–3925 ’ 2015 www.acsnano.org spot.[36,37] when difficulties are encountered in this situation, it is usually assumed that the signal detected is the average Raman scattering emanating from all of the graphene within the spot.[24,37,38]
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