Growth and characteristics of carbon nanotubes obtained under different C2H2/H2/NH3 concentrations

Aligned carbon nanotubes were synthesized under a combination of 20 different C2H2/H2/NH3 compositions at 700 °C using a thermal chemical vapor deposition method. Thin film Fe was used as the catalyst, which was pretreated with H2 or NH3 prior to the growth of carbon nanotubes. The use of different pretreatment gases results in little difference in the growth and characteristics of the carbon nanotubes except that the carbon nanotubes grown on H2 treated catalysts have smaller diameters. The growth rate of the CNTs does not depend on the NH3 concentration but on the ratio of NH3/C2H2. There is a critical NH3/C2H2 ratio that is independent of the C2H2 concentration and at which the peak growth rate occurs. The critical value was found to be 4.7 ± 1.2. Microstructural analysis indicates that the carbon nanotubes obtained at higher NH3 concentrations contain defects and disorder. Field emission tests show that the carbon nanotubes exhibit a turn-on field of 2.36 V/μm and a maximum current density of 1.91 mA/cm2. The field emission properties were found to be stable after 15 test cycles.