XPS and Raman characterization of single-walled carbon nanotubes grown from pretreated Fe2O3 nanoparticles

X-ray photoelectron (XPS) and Raman spectroscopic techniques have been used to study the influence of the annealing ambient (N2, Ar and H2) of nearly monodispersed Fe2O3 nanoparticles (mean size = 3.2 ± 1 nm) on the growth of carbon nanotubes by microwave plasma chemical vapour deposition. XPS characterization of the catalytic templates reveals that a N2 ambient reduces sintering of the Fe2O3 nanoparticles and confirms that the chemical phase involved in the nucleation of nanotubes is the metal state Fe0. Multi-excitation wavelength Raman spectroscopy (514, 574, 633 and 785 nm) reveals that the single-walled carbon nanotubes (SWCNTs) grown from N2-annealed catalyst nanoparticles range between 0.8 and 1.1 nm while SWCNTs grown from Ar-annealed catalyst nanoparticles exhibit a broader diameter distribution in the range 0.8–1.8 nm. The narrowness in the distribution of SWCNTs grown from the N2-annealed catalysts has been attributed to the enhanced stability of Fe2O3 nanoparticles in an N2 ambient. (Some figures in this article are in colour only in the electronic version)