Raman mapping of a single-layer to double-layer graphene transition D. Graf, F. Molitor, K. Ensslin, C. Stampfer, A. Jungen, C. Hierold and L. Wirtz Eur. Phys. J. Special Topics, 148 (2007) 171-176 Published online: 25 September 2007 DOI: 10.1140/epjst/e2007-00237-1