Synthesis of diameter controlled multiwall carbon nanotubes by microwave plasma-CVD on low-temperature and chemically processed Fe nanoparticle catalysts

Abstract

Properties of carbon nanotubes sensitively depend on the structural configuration, e.g., chirality, diameter, layer number and the compositional characteristics. The size of catalyst nanoparticles used to grow the CNTs significantly controls its diameter. Generally, catalyst nanoparticles are size-optimized via high-temperature annealing of thin metal films. Presently, formation of size-controlled Fe nano-particles as the efficient catalyst has been pursued via a low-temperature (TCG) wet chemical process that bypasses the high-temperature annealing step and leads to a low average size of catalyst nanoparticles. Suitable progress of the oxidation–hydrolysis reactions of metal-bearing ferrite entities controls the crystallinity via dehydration of the intermediate constituent and diminution of the oxide component. Optimally low diameter Fe nanoparticles have been obtained at temperature around TCG ~ +10 °C via simultaneous prominent aerial oxidation and neutralization in a single step. In this present work multiwall carbon nanotubes of controlled diameter (~15–25 nm) have been produced by relatively low-temperature (~300 °C) plasma processing, using pre-designed shadow-mask assembly to create diffused and remote-plasma of (CH4 + H2) and CO2 as a weak oxidizing gas to selectively remove the surplus amorphous components, and also by controlling the size of catalyst Fe-nanoparticles on the substrate via low-temperature non-plasma synthesis process.