Optical Absorption Properties of Single-Walled Carbon Nanotubes

Single-walled carbon nanotubes (SWNTs) are 1 dimensional (1D) tubular material with sp bonded graphene wall. Their unique geometry gives rise to sharp divergences in electronic density of states and consequently leads to characteristic discrete energy subbands. Since these inter-subband energy corresponds to near infrared (NIR) to visible (vis) range, many innovative optical application of SWNTs have been proposed thus far. The 1D geometry of SWNTs would be highly advantages for polarization-sensitive optical devices, provided their anisotropic optical absorption properties were appropriately understood. So far, quite few studies have investigated anisotropic optical absorption of SWNTs. Previous studies were done on weakly aligned SWNT films prepared by dispersing SWNTs in gel [1] or polymer matrices [2]. However, the measured range was limited only below 3.5 eV because of ultra-violet (UV) absorption of the employed matrix. Therefore, the well-known remarkable UV absorption of SWNTs, which forms absorption baselines in vis-NIR region, has not been examined deeply and thus not clarified well. In this study, using our vertically aligned SWNT (VA-SWNT) film directly grown a quartz substrate, we have elucidated polarization dependent optical absorption properties of SWNTs for wide energy range of 0.5 6 eV and explained origin of the remarkable UV absorption of SWNTs [3].