Boron-catalyzed multi-walled carbon nanotube growth with the reduced number of layers by laser ablation

Multi-walled carbon nanotubes with the reduced number of layers (2 or 3 layers) are dominantly produced by the laser ablation method using a carbon target mixed with boron. Chemical analysis with sub-nanometer resolution has revealed that the obtained nanotubes are composed of pure carbon layers with no boron concentration, while the boron carbide particle is found to be encapsulated at the nanotube tip. It is considered that the boron (in the form of boron carbide) acts as a catalyst during the nanotube formation. A critical particle size of the boron carbide for the tubular growth is found to be ∼5 nm.