Fine structure of the low-frequency Raman phonon bands of single-wall carbon nanotubes

The Raman spectra of single-wall carbon nanotubes produced by a laser and arc process were studied between 5 and 500 K. The linewidth versus temperature dependence of the low-frequency Raman bands between 150 and 200 cm−1 deviates from that expected for phonon decay through a phonon–phonon scattering mechanism. The experimental results and their analysis provide convincing evidence that each of the low-frequency Raman bands is a superposition of several narrower Raman lines corresponding to tubes of nearly the same diameter. At low temperatures the width Δ(T)=γ+Γ(T) of these components is determined mainly by the temperature-independent part γ≈2 cm−1.