Raman topography and strain uniformity of large-area epitaxial graphene

We report results of Raman spectroscopy studies of large-area epitaxial graphene grown on SiC. Our work reveals unexpectedly large variation in Raman shift resulting from graphene strain inhomogeneity, which is shown to be correlated with physical topography by coupling Raman spectroscopy with atomic force microscopy. We show that graphene strain can vary over a distance shorter than 300 nm and may be uniform only over roughly 1 microm. We show that nearly strain-free graphene is possible even in epitaxial graphene.