Abstract: Multi-wall carbon nanotubes were synthesized from C₂H₂ by chemical vapor deposition (CVD) method using LaNi₅ alloy micro-particles with diameters ranging from 41 to 150 μm as catalyst. Electron spin resonance (ESR) spectra of purified carbon nanotubes were acquired at different temperatures between 100 and 290 K. The effects of the size of the catalyst particles used and addition of hydrogen gas during synthesis on the ESR characteristics (i.e., line shape, g-value and linewidth) of the produced nanotubes were investigated. It was found that the g-values of the produced nanotubes increase with their diameters: nanotubes having diameters between 10 and 20 nm (synthesized with catalyst particles having diameters between 41 to 50 μm) have an averaged g of 2.0400, while those having diameters between 70 and 120 nm (synthesized with catalyst particles having diameters between 100 to 150 μm) have an averaged g of 2.0898. It was also found that there is only one peak in the ESR spectra of carbon nanotubes with small diameters, while the nanotubes having larger diameters show two peaks, and the intensity of the additional peak increases with temperature.

Key words: ESR, carbon nanotube, chemical vapor deposition, LaNi₅ alloy micro-particle