Raman mapping of a single-layer to double-layer graphene transitionD. Graf, F. Molitor, K. Ensslin, C. Stampfer, A. Jungen, C. Hierold and L. WirtzEur. Phys. J. Special Topics, 148 (2007) 171-176DOI: https://doi.org/10.1140/epjst/e2007-00237-1