Formation of Bamboo-Like Carbon Nanotubes and Nanofibers Using Co–Si–O and Co–Si Catalysts

Bamboo-like carbon nanotubes were synthesized by microwave plasma chemical vapor deposition (MPCVD) using CH₄ and N₂ as source gases in various ratios. Two types of catalytic films, namely, a condition 1, Co film/SiO₂/Si substrate, and, a Co film/Si substrate layer with rapid thermal annealing (RTA; condition 2), were used as catalysts to grow carbon nanotubes. The interaction between the catalytic film and the Si substrate or between the catalytic film and the SiO₂ interlayer occurred during the H₂ reduction step before nanotube growth. The chemical compositions of catalytic particles capping the carbon nanotubes were identified by energy-dispersive X-ray spectroscopy (EDS) as Co–Si–O and Co–Si for conditions 1 and 2, respectively. The growth of the base and tip growths was investigated and is suggested to be governed by the capillary effect and the strength of adhesion between the catalytic particles and the underlayer. Transmission electron microscopy (TEM) analysis reveals that the carbon nanotubes and nanofibers have bamboo-like structures with hollow internal compartments. The formation mechanisms of these bamboo-like structures are discussed.