  Mechanical properties of graphene prepared by chemical vapor deposition (CVD)
are not easily comparable to the properties of nearly perfect graphene prepared
by mechanical cleavage. In this work, we attempt to investigate the mechanical
performance of CVD graphene (simply supported or embedded in polymer matrix),
transferred by two different techniques, under uniaxial loading with
simultaneous in-situ monitoring by Raman microspectroscopy. The level of charge
transfer doping and strain is assessed using the vector analysis modified for
uniaxial strain. The strain distribution across the samples varies
significantly, owing to the growth and transfer process, which induces wrinkles
and faults in the CVD graphene. In simply supported specimens, the stress
transfer efficiency is generally very low and the changes in Raman spectra are
dominated by variations in the charge transfer originating from the realignment
of the domains on the substrate upon the application of strain. In contrast,
samples covered with an additional polymer layer exhibit an improved stress
transfer efficiency, and the alterations of charge doping levels are
negligible. In fully embedded specimens, the variations in stress transfer
efficiencies are caused by the size of the effective graphene domains defined
by cracks, folds and or/wrinkles.
