Far-infrared gaps in single-wall carbon nanotubes

Abstract

The infrared properties of single-wall carbon nanotubes have been measured over 15–5000 ${\mathrm{cm}}^{\mathrm{-}1}$. The sample is a freestanding film composed of purified nanotubes. The temperature dependence of the reflectance is quite small at all temperatures studied (7.8 to 298 K) and no vibrational features are observed. The spectrum has a clear plasma edge, analyzed by a Drude model combined with a low-frequency localized absorption at 135 ${\mathrm{cm}}^{\mathrm{-}1}$. The absorption band is assigned to a pseudogap in armchair nanotubes and/or to very small gaps in zigzag or chiral nanotubes.