How doping and defects alter linewidths and lifetimes of G-band optical phonons, in carbon nanotubes is examined. Optical phonon lifetimes, T 1, in thin films of nanotubes are measured by 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 in this study, T1 does not appear to change. A varying degree of doping in individual nanotubes by means of electrostatic gating reveals decreasing full-width at half-maximum Γ down to ∼4 cm-1 at the charge neutrality point. Increasing disorder, on the other hand, leads to a decrease in T1 along with an increase in Γ. We observe a decrease in T1 of ∼0.4 ps at an estimated effective crystallite size La ∼ 130 nm based on 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 coincides with a lifetime broadening of ∼4 cm-1 based on a measured T1 of 1.2 ps. Samples displaying different degree of metallic or semiconducting contributions in their static Raman spectrum are also compared and are shown to exhibit similar values of T1.
|Original language||English (US)|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - May 20 2011|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics