  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.
