Polarization dependent optical absorption properties of single-walled carbon nanotubes and methodology for the evaluation of their morphology

Polarization dependence of the optical absorption properties of SWNTs is presented and investigated in detail for the energy range 0.5-6 eV. We found that the absorption peaks in the UV region at approximately 4.5 and 5.25 eV exhibit remarkable and different dependencies on the morphology of the SWNT film, or equivalently, on the incident light polarization relative to the SWNT axis. An analytical pathway to evaluate the physical degree of SWNT alignment for a vertically aligned SWNT film is developed with both transition dipoles parallel and perpendicular to the SWNT axis taken into account. This analytical procedure, coupled with polarized optical absorption measurements performed on the vertically aligned SWNT film grown on substrates, leads to the determination of the bare optical absorption cross-section of SWNTs for both parallel and perpendicular to SWNT axis. In the end, the proposed methodology for evaluating the SWNT film morphology is applied to investigate the transient change of the degree of alignment in the growth process of our vertically aligned SWNT films.