RAMAN SCATTERING OF CARBON NANOTUBES

The present state of Raman scattering from carbon nanotubes is reviewed. In the first part of the presentation, the basic concepts of Raman scattering are elucidated with particular emphasis on the resonance scattering. The classical and the quantum-mechanical descriptions are presented and the basic experimental instrumentation and procedures are described. Special Raman techniques are discussed. Eventually, a short review on the electronic structure of single-wall carbon nanotubes (SWCNTs) is given. The second part of the presentation deals with Raman scattering from SWCNTs. The group theoretical analysis and the origin of the basic Raman lines are described. For the radial breathing mode, the observed quantum oscillations and the unusual strong Raman cross section are discussed. For the G-line, the resonance behavior and the response to doping are demonstrated and the calculated dependence of the line frequency on the tube diameter is summarized. For the D-line and for the G’-line, the dispersion is demonstrated and its origin from a triple resonance mechanism is described. Finally, the response from pristine and doped peapods is elucidated. In the third part, most recent results are reported from Raman spectroscopy of double-wall carbon nanotubes (DWCNTs). The unusual narrow lines with widths down to 0.4 cm-1 indicate clean room conditions for the growth process of the inner tubes. The (n,m) assignment of these lines and the high curvature effects are discussed. Results for DWCNTs, where the inner tubes are highly 13C-substituted, are reported with respect to Raman and NMR spectroscopy. Eventually, it is demonstrated that the RBM Raman lines of the inner tubes cluster into groups of up to 14 lines where each member of the cluster represents a pair of inner-outer tubes.