Simon, F. and Zolyomi, V. and Pfeiffer, R. and Kuzmany, H. and Koltai, J. and Kurti, J. (2010) Unusual Raman dispersion for D and 2D lines in high-curvature single-walled carbon nanotubes revealed by C-13 isotope substitution. Physical review B, 81 (12): 125434. ISSN 1098-0121
Abstract
The defect-induced D line and its overtone are fundamental signatures in the Raman spectra of carbon nanomaterials. An analysis of these lines as a function of laser excitation energy is reported for double-walled carbon nanotubes where the inner tubes represent high-curvature nanotube species. From 13C substituted inner tubes it is demonstrated that the quasilinear relations between laser energy and line position (Raman dispersion) cross over unexpectedly for low-energy excitation for the inner and outer tube shells. The result is quantitatively explained by a curvature-induced phonon softening and first-principles calculations of the optical transition energies.