Ion irradiation-induced, localized sp2 to sp3 hybridized carbon transformation in walls of multiwalled carbon nanotubes

In this report, ion irradiation-induced localized sp2 to sp3 hybridized carbon transformation in multiwalled carbon nanotubes (MWCNTs) was observed after irradiating MWCNTs with high-energy Au+8 ions (100 MeV). The used MWCNTs were grown using cobaltocene and benzene as catalyst and carbon source, respectively by the thermal CVD technique and consist of both unfilled and Co-filled tubes. Prior to irradiation, the MWCNT sample was characterized using scanning electron microscope and micro-Raman and photoluminescence spectrometers. The effect of ion fluence on MWCNT walls and transformation of sp2 to sp3 sites was analyzed by Raman spectroscopy, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. We found that as the fluence increased, the localized transformation from sp2 to sp3 sites occurred in the walls of MWCNTs, which was evident by the emergence of peak at approximately 1543 cm−1 associated with the G peak in tetrahedral amorphous carbon (ta-C) and the vanishing of 2D band (2700 cm−1). Furthermore, we observed broadening in D and G, with slight shift in their positions and consistent decrease in 2D band intensity, as fluence increased.