The optical spectra of carbon nanotubes

Single wall carbon nanotubes (SWCNs) of mono size and unique chirality are formed inside micro-channel array of a zeolite single crystal. Since they are forced to align along the c-axis of the crystal, they show strong polarization anisotropy in the optical absorption from near infrared to visible region. We have developed an effective and systematic way to measure the UV- FIR polarized optical absorption spectrum of nanotubes. The polarization anisotropy of SWCNs in the infrared were studied by using the technique of Fourier Transform Infrared Spectroscopy (FTIR). Polarized optical absorption spectra in UV-NIR of SWCNs were measured with conventional dispersive spectrometry. We observed strong polarization anisotropy of the samples and carbon nanotubes are well arrayed in the zeolite. Absorption peaks with energy at 1.78eV and 3.4eV are being observed when the light electric field (E) is parallel to the tube direction (C), which are attributed to the inter-band transition of the nanotubes. This result agrees well with the calculation of density of state based on the local density function approximation