Raman Topography and Strain Uniformity of Large-Area Epitaxial Graphene
  We report results from two-dimensional Raman spectroscopy studies of large-area epitaxial graphene grown on SiC. Our work reveals unexpectedly large variation in Raman peak position across the sample resulting from inhomogeneity in the strain of the graphene film, which we show to be correlated with physical topography by coupling Raman spectroscopy with atomic force microscopy. We report that essentially strain free graphene is possible even for epitaxial graphene. 
J. A. Robinson, C. P. Puls, N. E. Staley, J. Stitt, M.A. Fanton, K. V.   Emtsev, T. Seyller, Y. Liu