Finally, the Raman spectrum of the as-grown MWCNTs synthesized at the optimum conditions is shown in Fig. 12. Both a G-band corresponding to the Raman scattering mode of sp2-hybridized carbon at 1592 cm−1 and a D-band attributed to carbonaceous particles, indicating the presence of defects in the graphite structure at around 1297 cm−1, were present. The ratio of the intensities between the two peaks (ID/IG) was measured to be ca. 1.13, which is in close agreement with previous reports on MWCNT synthesis.