The manner in which doping and defects alter the linewidths and lifetimes of G-band optical phonons in carbon nanotubes was examined. Optical phonon lifetimes, T1, in thin films of nanotubes were measured using time-resolved incoherent anti-Stokes Raman spectroscopy and considered along with Raman linewidths of isolated individual nanotubes. Within the doping range achievable in nanotube films, T1 did not appear to change. A varying degree of doping in individual nanotubes by means of electrostatic gating revealed a decreasing full-width at half-maximum Γ down to ∼4/cm at the charge neutrality point. Increasing disorder, on the other hand, led to a decrease in T1 together with an increase in Γ. A decrease in T1 of ∼0.4ps was observed at an estimated effective crystallite size La ∼ 130nm based upon the D-band to G-band peak intensity ratio. In the limit of zero doping and zero defects, the measured Γ of single semiconducting nanotubes coincided with a lifetime broadening of ∼4/cm based upon a measured T1 of 1.2ps. Samples displaying various degrees of metallic or semiconducting contributions in their static Raman spectrum were also compared and were shown to exhibit similar values of T1.

Influence of Defects and Doping on Optical Phonon Lifetime and Raman Linewidth in Carbon Nanotubes. D.Abdula, K.T.Nguyen, K.Kang, S.Fong, T.Ozel, D.G.Cahill, M.Shim: Physical Review B, 2011, 83[20], 205419