Single-walled and multi-walled carbon nanotubes grown by chemical vapor deposition were studied using high-resolution transmission electron microscopy, Raman scattering and photoluminescence, electron spin resonance and thermogravimetric analysis. Raman spectra of both single-walled carbon nanotubes and multi-walled carbon nanotubes revealed additional features in the frequency range intermediate between 600 to 1300/cm and 1700 to 2600/cm; in addition to well-known radial breathing modes, D- and G-bands. Room-temperature photoluminescence studies revealed two broad but distinct peaks centered at ∼2.05 and ∼2.33eV, for both single-walled carbon nanotubes and multi-walled carbon nanotube samples. Thermogravimetric analysis indicated a very low impurity content in multi-walled carbon nanotube samples as compared to single-walled carbon nanotube samples. High-resolution transmission electron microscope analysis revealed various kinds of structural defects in nanotube walls. With the aid of high-resolution transmission electron microscopy and electron spin resonance studies, it was argued that the intermediate frequency Raman modes and the visible photoluminescence from the pristine nanotubes were definite signatures of structural defects in the nanotubes.

Optical Signature of Structural Defects in Single Walled and Muitiwalled Carbon Nanotubes. D.K.Singh, P.K.Iyer, P.K.Giri: Journal of Nanoscience and Nanotechnology, 2009, 9[9], 5396-401