Probing carbon isotope effects on the Raman spectra of graphene with different 13C concentrations

A resonance Raman study of graphene samples with different C-13 isotopic concentrations and using different laser excitation energies is presented. The main Raman peaks (D, G, G*, and 2D) of graphene were measured and the dependence of their frequencies on the isotope atomic mass follows a simple harmonic oscillator relation. The G* and 2D double-resonance peak positions were measured as a function of the laser energy, and we observed that the slopes of the laser energy dependence are the same independently of isotope concentration. This result shows that isotopic substitution does not alter the electron and phonon dispersions near the K point of the graphene Brillouin zone. From the linewidth of G and 2D Raman peaks, we have also obtained a dependence of the phonon lifetime on the C-13 isotope concentration.