Resonant Raman spectroscopy on enriched 13C carbon nanotubes Original Research Article

Isotopically enriched single-wall carbon nanotubes with different 13C concentrations were investigated by resonant Raman spectroscopy. Linear reductions of the Raman frequencies with an increase of 13C concentration are observed for the different nanotube Raman modes, and the effect of the reduced mass variation of the isotope mixture on the phonon frequencies is described through a simple harmonic oscillator model. In addition to the frequency dependence, the Raman linewidths as a function of the 13C concentration were also investigated and an expression describing this is presented. We observe an increase in the G band linewidth, as the 13C:12C ratio approaches unity. Measurements with different excitation energies were performed and the frequency dispersions of the D and G′ bands with laser energy were observed to be the same for 12C and 13C nanotubes, suggesting no changes in the electronic structure after isotope enrichment. Through analysis of the radial breathing modes in the Raman spectra obtained with different excitation energies, a relation between these modes frequency and the 13C nanotubes diameter was also established.