  Accurate and simple local strain assessment in graphene is one of the crucial
tasks in device characterization. Raman spectroscopy is often used for that
purpose through monitoring of the G and 2D modes. However, the shifts of those
two bands might be biased, especially under uniaxial strain, by the effects of
charge-transfer doping. Therefore, it is extremely desirable to use another
Raman band, less affected by doping, but with a defined and measurable behavior
under strain. The Raman 2D' mode is in this sense the ideal feature for the
evaluation of strain levels in stretched graphene monolayers, suitable for this
task even under different experimental conditions. The sensitivity and accuracy
of the approach through 2D' mode is on the same level as through the G mode,
however, the clear advantage of the 2D' arises when doping effects are present
in the sample.
