Effect of Catalyst Film Thickness on the Growth, Microstructure and Field Emission Characteristics of Carbon Nanotubes

Aligned multiwalled carbon nanotubes (CNTs) were grown by microwave plasma enhanced chemical vapor deposition on Si substrates using C₂H₂ and NH₃ gas mixture. Effect of Fe film thickness (5-30 nm) on the growth, microstructure and field emission characteristics of CNT films were investigated. Both Fe particle size and CNTs diameter increased with Fe thickness but CNTs length decreased. CNTs grown up to a Fe thickness of 20 nm, were found to have mainly well arranged bamboo-structures. However, for higher Fe thickness, CNTs were found to have mostly dual structural feature (solid fiberlike + bamboo- structure). It is suggested that relative rates of bulk and surface diffusions of carbon, which is catalyst size dependent, are responsible for such structural features. Field emission measurements of the CNT films showed turn-on field to be 1.6-3.2 V/ mum.