X-ray induced defects in single-walled and double-walled carbon nanotubes were characterized by Raman scattering spectroscopy. Frenkel defects, interstitial-vacancy pairs, were revealed to form in both single-walled carbon nanotubes and double-walled carbon nanotubes after X-ray irradiation because these defects were entirely healed by thermal annealing. In order to clarify the structure of the X-ray induced defect in single-walled carbon nanotubes and double-walled carbon nanotube, isochronal-annealing experiments were performed on the irradiated samples and the activation energy for defect healing was estimated. The intensity of D band (defect induced band) on Raman spectra was used as a measure of the density of X-ray induced defects. The experimental results were in good agreement with the simulated values using second-order reaction model, which indicated that the defect healing was determined by the migration energy of interstitials on the carbon layer. It was also found that the activation energy for defect healing of single-walled carbon nanotubes and double-walled carbon nanotube were around 0.5 and 0.32eV, respectively. The X-ray induced defects in single-walled carbon nanotubes were more stable than those in double-walled carbon nanotubes. Compared these estimated activation energies to previous theoretical reports, it was concluded that bridge and/or dumb-bell interstitials were formed in both single-walled carbon nanotubes and double-walled carbon nanotubes by X-ray irradiation.

Isochronal Annealing Study of X-Ray Induced Defects in Single- and Double-Walled Carbon Nanotubes. T.Murakami, Y.Yamamoto, K.Kisoda, C.Itoh: Journal of Applied Physics, 2013, 114[11], 114311