G^′ band Raman spectra of single, double and triple layer graphene

We have measured the Raman spectra of one to three layer graphene as a function of laser excitation energy. The observed G^′ band Raman peak (∼2650 cm^-1) intensity decreases with increasing numbers of graphene layers. The electronic energy band structure calculated by the extended tight binding model shows that there are four and nine possible optical processes in double resonance theory for the Raman G^′ band of double and triple layers graphene, respectively. Raman intensity calculations show that each peak position depends on its wavevector, and then the G^′ band of double and triple layer graphene has three and five components, respectively.