Study of charge dynamics in transparent single-walled carbon nanotube   films
  We report the transmission over a wide frequency range (far infrared - visible) of pristine and hole-doped, free-standing carbon nanotube films at temperatures between 50 K and 300 K. Optical constants are estimated by Kramers-Kronig analysis of transmittance. We see evidence in the far infrared for a gap below 10 meV. Hole doping causes a shift of spectral weight from the first interband transition into the far infrared. Temperature dependence in both the doped and undoped samples is restricted to the far-infrared region. 
F. Borondics (1), K. Kamaras (1), M. Nikolou (2), D. B. Tanner (2), Z.   H. Chen (2), A. G. Rinzler (2) ((1) Research Instit...