Synthesis of single-walled carbon nanotubes over a spin-coated Fe catalyst in an ethanol–PEG colloidal solution Original Research Article

Single-walled carbon nanotubes (SWCNTs) have been grown on flat silicon oxide substrates by the decomposition of methane. The spin-coated iron(III) nitrate with a concentration of 40 mmol/L diluted in a colloidal solution with ratio 1:1 (v/v) of absolute ethanol to PEG-400 was found to form iron nanoparticles that are small enough to grow SWCNTs. The role of PEG was to interact with iron ions and encapsulate the iron, thus preventing agglomeration, while the absolute ethanol isolated the PEG–iron micelles. The ratio of absolute ethanol to PEG controlled the viscosity and the distance between PEG–encapsulated iron micelles, and subsequently governed the size and density of the iron nanoparticles formed. To reduce the effect of surface tension that will disturb the uniformity of a thin colloid film, –OH groups were introduced on the silicon wafer by a piranha solution and the hydrogen bonds formed with PEG preserved the uniformity of the iron nanoparticle distribution during the synthesis of SWCNTs.