Polarization Effects of Transversal and Longitudinal Optical Phonons in Bundles of Multiwall Carbon Nanotubes

We report on the polarization analysis of the Raman spectrum of highly vertically aligned multiwall carbon nanotubes (MWCNTs). A simple model considering the average angle distribution across the MWCNT axes accounts for the observed angular dependent Raman mode intensity. The model fully fits the experimental data, allowing to derive an average waving angle of similar to 37 degrees around the MWGNT axes and explaining the apparent discrepancy of previous experiments reported in the literature. Furthermore, we can distinguish two components in the Raman G-band, associated to the longitudinal and transversal optical modes. Their intensity dependence as a function of polarization clearly suggests the metallic nature of these MWCNTs, experimentally verified by the valence band photoemission analysis. The present study provides a simple, effective spectroscopic method to determine physicochemical and specific morphological characteristics of carbon nanotubes.