Far-infrared to visible optical conductivity of single-wall carbon nanotubes

The reflectance of unoriented single-wall carbon nanotube films has been measured over a wide wavelength range (far-IR-UV). The results are consistent with the film being a mixture of conducting (armchair), small bandgap (n≡m, mod 3) and semiconducting nanotubes. The optical conductivity shows peaks corresponding to transitions between density-of-states peaks of these tubes, at energy locations consistent with 1.4 nm diameter tubes. In addition optical absorption spectroscopy of aligned single-wall carbon nanotubes shows that the optical transitions are well-aligned along the tube axis. This behavior is consistent with polarized resonant Raman and electronic structure calculations.