Length dependence of the Raman spectra of carbon nanotubes

[摘要] (cont.) When the spectra are divided in this way, we have found that the properties of the various Raman peaks differ significantly between the two groups. We have found that the Raman spectra, especially for metallic nanotubes, varies for different spots on the same sample. This results in noisier data, for which the trends are not clear. We describe the use of the linear correlation analysis method, which allows correlations to be identified despite noisy data. For several of the Raman features, we have found that metallic nanotubes appear to be more sensitive to length than semiconducting tubes. From our analysis of the G-band, electron-phonon coupling seems to decrease for shorter nanotubes. The correlations between the different G-band parameters (frequency, linewidth, normalized intensity, and asymmetry) were identified. The D-band, which arises from a breakdown in selection rules brought about by finite size effects, was found to have a normalized intensity (relative to the G+ peak) that is inversely proportional to the nanotube length. We observe that the G;; feature is comprised of two peaks, which is a result of two energy levels being simultaneously excited. Although the G* peak was weak and noisy, a few length dependent effects above the noise level were observed. Finally, we also observed some length dependence in the RBM peak.

[发布机构] Massachusetts Institute of Technology