Defects were systematically introduced into the body of a multi-walled carbon nanotube by using an acid treatment, and the evolution of the defects was monitored by Raman spectroscopy using various excitation wavelengths. The D and D’ modes were most prominent and responsive to defect formation caused by acid treatment. They exhibited a dispersive behavior upon changing the excitation wavelengths, as expected from the double-resonance Raman mechanism. Several weaker Raman resonances, including D" and L1(L2)+D’ modes, were also observed at the lower excitation wavelengths (633 and 785nm). In addition, specific structural defects including the typical pentagon-heptagon structure (Stone-Wales defects) were identified by Raman spectroscopy. Closer analysis revealed Haeckelite structures: specifically the Ag mode response in R5,7 and O5,6,7.

Defect-Induced Vibrational Response of Multi-Walled Carbon Nanotubes using Resonance Raman Spectroscopy. S.A.Curran, J.A.Talla, D.Zhang, D.L.Carroll: Journal of Materials Research, 2005, 20[12], 3368-73