Vertically aligned multiwalled carbon nanotubes were synthesized by electron cyclotron resonance chemical vapor deposition on Ni-coated glass substrates at temperatures as low as 400 °C. Negative self-biases were induced to the substrates by radio frequency plasma to give ion bombardment to the growing surface. An increase of self-bias voltages from −50 to −200 V resulted in an evolution of the microstructures from amorphous carbon to nanorods, subsequently to nanotubes. Nanotubes grown above −150 V were more straight in morphology and better in crystallinity than nanorods grown at −100 V. In the field emission (FE) measurements, the electric fields to obtain 1 μA/cm2 were 4.6 and 11.1 V/μm for the nanorods and nanotubes grown at −100 and −200 V, respectively. The emission areas, calculated from the Fowler–Nordheim plots, were much larger in the nanorods than the nanotubes. It is considered that a larger amount of crystalline defects in nanorods plays a major role in improving their FE characteristics.

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