Tunable Raman spectroscopy study of CVD and peapod-derived bundled and individual double-wall carbon nanotubes

We use 40 laser excitation energies to analyze the differences in the Raman spectra from chemical vapor deposition-derived double-wall carbon nanotube (CVD-DWNT) bundles, fullerene-derived DWNT bundles (C₆₀ -DWNTs), and individual fullerene-derived DWNTs with inner type-I and type-II semiconducting tubes paired with outer metallic tubes. For the radial breathing mode (RBM) of SWNTs, an experimental ω_RBM vs d_t relationship of the form ω_RBM =A/ d_t +B is obtained for the inner tubes of DWNT bundles where the A and B constants are found to be close to those obtained by elasticity theory when modeling the elastic properties of graphite. A similar change in ω_RBM is observed for an inner type-II semiconducting (6,5) tube and a type-I (9,1) tube when inside various metallic outer tubes. The G-band frequency is observed to upshift when switching the laser resonance from DWNTs with semiconducting inner tubes to DWNTs with metallic inner tubes. Finally, we measure the G⊃′ feature from C ₆₀ -DWNTs and note a downshift in frequency with respect to that of CVD-DWNTs.