We present a resonance Raman study of the disorder-induced D mode in a sample highly enriched with semiconducting (9,7) single-walled carbon nanotubes in the excitation energy range of 1.49 − 2.05 eV. The intensity of the D mode shows a resonance behavior near the optical transition of the (9,7) tube. The well-known dispersion of the D-mode frequency, on the other hand, is not observed at the resonance, but only above a certain excitation energy. We explain our results by numerical simulations of the D-mode spectra.

We analyze the defect-induced Raman mode (D mode) and the second order 2D mode of samples enriched with metallic and semiconducting single-walled carbon nanotube (SWCNT). By resonance Raman spectroscopy, we study the evolution of the line shape of the D and 2D mode. We compared the radial-breathing mode (RBM) frequencies with different components of the D and 2D mode in the enriched samples and a non-enriched SWCNT reference material. We show that the components of the broad D mode can be assigned to different species of nanotubes and that this assignment is not necessarily correlated to the RBM for the same excitation energy.Raman intensity of the 2D mode for differently enriched samples and comparison with a reference sample. The gray spectrum is the sum of the spectra from the enriched samples.

Covalent functionalization of single-walled carbon nanotubes typically leads to an intensity increase of the defect-induced Raman mode (D mode). A large intensity ratio of the D and G modes (D/G ratio) is therefore often used as evidence for a successful functionalization. Here, we discuss the effect of the D-mode resonance on the D/G ratio and compare pristine and covalently functionalized nanotubes. By resonance Raman spectroscopy we study the evolution of the lineshape and frequencies of the D and 2D modes of samples enriched with semiconducting and metallic nanotubes in comparison with the radial breathing mode. First, we experimentally demonstrate

We present a theoretical model to describe the double-resonant scattering process in arbitrary carbon nanotubes. We use this approach to investigate the defect-induced D mode in CNTs and unravel the dependence of the D-mode frequency on the CNT diameter and on the energy of the resonant optical transition. Our approach is based on the symmetry of the hexagonal lattice and geometric considerations, hence the method is independent of the exact model that is chosen to describe the electronic band structure or the phonon dispersion. We finally clarify the diameter dependence of this Raman mode that was controversely discussed in the past and demonstrate that, depending on the experimental conditions, in general two different dependencies can be measured. We also prove that carbon nanotubes with arbitrary chiral index can exhibit a D mode in their Raman spectrum, in contrast to previous symmetry-based arguments. Furthermore, we give a direct quantification of the curvature-induced phonon frequency corrections of the D-mode in carbon nanotubes with respect to graphite.

We present the Raman bands of nano-graphene flakes (NG flakes) produced by oxidation of single-walled carbon nanotubes. These bands overlap with the defect-induced Raman modes of carbon nanotubes. This can lead to an overestimation of the defect density in the nanotubes. Here we analyze the line shape and the dispersion of this superimposing Raman band of NG flakes. Furthermore, we investigate the predicted Raman\ud band of NG flakes next to the high-energy Raman modes (G− and G+) of the nanotubes