Contribution of the buffer layer to the Raman spectrum of epitaxial   graphene on SiC(0001)
  We report a Raman study of the so-called buffer layer with $(6\sqrt3\times6\sqrt3)R30^{\circ}$ periodicity which forms the intrinsic interface structure between epitaxial graphene and SiC(0001). We show that this interface structure leads to a nonvanishing signal in the Raman spectrum at frequencies in the range of the D- and G-band of graphene and discuss its shape and intensity. Ab-initio phonon calculations reveal that these features can be attributed to the vibrational density of states of the buffer-layer. 
F. Fromm, M. H. Oliveira Jr, A. Molina-S\'anchez, M. Hundhausen, J. M.   J. Lopes, H. Riechert, L. Wirtz, T. Seyller
cond-mat.mtrl-sci