High-pressure Raman response of single-walled carbon nanotubes: Effect of the excitation laser energy

Abstract

We report high-pressure Raman experiments on the tangential vibrational modes of CarboLex bundled single-walled carbon nanotubes up to 6.5 GPa using two different excitation energies: 1.96 and 2.41 eV. We show through the curve-fitting technique, together with the modified interband transition energies versus diameter plot, how the nature of the resonant tubes is modified under the excitation energy, in particular under the 1.96 eV excitation. Having metallic and semiconducting tubes in resonance at ambient pressure, we find that only semiconducting tubes are in resonance at 3.5 GPa. We associate this loss of resonance from the metallic tubes to a redshift pressure response of the first $({E}_{11})$ transition energies from these tubes. Added to that, the change in the excitation energies leads to a change in the value of the transition pressure. This is simply associated with the fact of having different diameters in resonance under each excitation from the same sample.