▎ 摘　　要

In contrary to the widely reported single and symmetric peak feature of G' band in Raman spectrum of graphene, we herein report the observation of splitting in G' band in free standing graphene. Our experimental findings provide a direct and strong support for the previous theoretical prediction that the coexistence of the outer and inner processes in the double-resonance Raman scattering would cause the splitting of G' mode. The investigation of the influence of trigonal warping effect on the spectral features of G' subbands further verified the theoretical interpretation established on the anisotropic electronic structure of graphene. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4729407]