Observation of the diameter-dependent Raman dispersion effect in chemically oxidized multiwalled carbon nanotubes

Chemical oxidation of multiwalled carbon nanotubes (MWCNTs) using H2SO4/HNO3 solution has been monitored by micro-Raman spectroscopy and X-ray absorption spectroscopy. The diameter distribution variation in MWCNTs due to chemical oxidation has been measured by scanning electron microscopy and transmission electron microscopy. The Raman dispersion behaviors of the intensity ratio and the band positions of the D, G, and G' bands were found to be correlated with the MWCNT diameter distribution. It was also found that, during the nanotube unzipping process, defect formation complicates the observation of the diameter-dependent Raman dispersion effect. The curvature effect plays an important role in the intensity ratio trend. On the other hand, defect formation dominates the band position trend. (C) 2011 Elsevier Ltd. All rights reserved.