A study was made of the effect of 30keV N+ ion irradiation to three fluences, 1012, 1013 and 1014/cm2, upon the structural and spectroscopic properties of single-walled and multi-walled carbon nanotubes. Irradiation-induced structural defects and coalescence of the nanotubes were studied using high-resolution transmission electron microscopy. Upon irradiation, some of the radial breathing modes in Raman spectra disappeared due to conversion from single-walled to multi-walled structure. A systematic change in intensity of the intermediate frequency mode was observed with increasing dose of ion-irradiation and these intermediate frequency modes were attributed to structural defects of single-walled carbon nanotubes. A marked improvement in the intensity ratio G-band to D-band (at ∼1335/cm) for ion fluences of 1013ions/cm2 indicated an improved graphitic structure as a result of reconstruction. Similarly, X-ray photo-electron spectroscopy revealed an improvement in the amount of sp2 carbon after a 1013/cm2 N+ ion-irradiation dose. At a higher dose (1014N+/cm2), vacancy and bent structures having Stone-Wales defects were observed in high-resolution transmission electron microscopy, whereas multi-walled carbon nanotubes showed the formation of surface hillock like protrusions leading to the formation of fullerene-like structures.

Defect Evolution and Structural Improvement in Low Energy Ion Irradiated Carbon Nanotubes: Microscopic and Spectroscopic Studies. D.K.Singh, P.K.Iyer, P.K.Giri: International Journal of Nanoscience, 2011, 10[1-2], 49-53