Effects of Ion Beam Irradiation on Thermal Oxidation of Single Walled Carbon Nanotubes

The properties of carbon nanotubes (CNTs) are closely dependent on their structures, and therefore may be tailored by controllably introducing defects in the nanotube systems. In this work, we investigate the effects of energetic ions (H$_{2}$, He and Ne) on the thermal stability of single wall nanotubes (SWNTs) against oxidation in air. SWNTs were irradiated with ions of energy in MeV to various doses in the range of 10$^{13 }$- 10 $^{16}$ cm$^{-2}$. Thermogravimetric analysis was used to determine the loss of CNT masses within 300-700 $^{o}$C as a result of oxidation processes. As opposed to the case of pristine SWNTs, the temperature (T$_{m})$ corresponding to maximum oxidation rate was increased by about 25 $^{o}$C for the SWNTs implanted with Hydrogen dose of 10$^{15}$ cm$^{-2}$, while He and Ne ion implantation resulting in decrease in T$_{m}$. The activation energies for thermal oxidation under various conditions were also extracted from TGA data, with values ranging from 1.13 eV (for pristine SWNTs) to 1.37 eV, depending on ion doses and species. Raman spectroscopy was used to determine the characteristics of the G band (C-C stretching mode) and D band (disorder induced mode) in CNTs. The work suggests that the bonding in CNTs could be strengthened or weakened depending on the amount of ion-beam- induced defects, leading to the enhanced or reduced thermal stability of CNTs against oxidation.