Spectroscopic study of carbon nanotubes

We present a comprehensive experimental study of the vibrational spectra of nanotubes. There are two main lines observed in the Raman spectrum, one positioned at 1350 cm^-1, the D lire, and the other at 1580 cm^-1, the G line. Both these lines are very similar to those seen with disordered graphite. The disorder induced D line is very weak compared to the G line which i indicative of high crystalline materials. The position and intensity of the D line strongly depends on the energy of the exciting laser. This dispersion effect was also observed for graphitic particles and may be explained by a photoselective resonance process of nanowbes with different sizes. There are two optically active modes in the Infrared spectrum for highly orientated polycrystalline graphite (HOPG) which are the E_1u and A_2u modes. The Ei mode is positioned at 1587 cm^-1 while the A_2u mode is positioned at 868 cm^-1. The Infrared spectrum of the nanotubes shows both modes although the E_1u mode is downshifted to 1575 cm^-1