Morphology, diameter distribution and Raman scattering measurements of double-walled carbon nanotubes synthesized by catalytic decomposition of methane

Double-walled carbon nanotubes (DWNTs) were synthesized by catalytic decomposition of methane in the presence of Fe catalyst at 1373 K. The microstructure of the as-prepared DWNTs was characterized by high-resolution transmission electron microscopy (HRTEM) and resonant laser Raman spectroscopy. HRTEM observations revealed that the dominant type of the as-prepared product was DWNTs, which are mostly bundle-like. A triangular lattice arrangement of DWNTs in a DWNT bundle was observed. The as-prepared DWNTs show corresponding peaks from resonant Raman spectra of the radial breathing mode (RBM), which are considered to be associated with inner tubes as well as outer tubes of the DWNTs. The outer and inner tube diameters of the DWNTs, as determined from HRTEM images, are in the range of 1.6–3.6 and 0.8–2.8 nm, in agreement with the results from the resonant Raman scattering measurements. Moreover, the interlayer spacing of DWNTs is not a constant, ranging from 0.34 to 0.41 nm.