Carbon nanofiber bundles were vertically well-grown on a nickel-coated silicon substrate from the microwave plasma-enhanced chemical vapor deposition under the application of high negative bias voltage. The formation of carbon nanofiber bundles was systematically investigated as a function of the reaction time. At the initial stage of the reaction, many submicrometer-sized grains having bamboo sprout-like shape were developed. Carbon nanofiber bundles formation was initiated at the top position of each bamboo sprout-like shaped grains. Subsequent carbonization reaction produced longer and thicker carbon nanofiber bundles. Each carbon nanofiber bundle was composed of several tens nanometer-sized individual carbon nanofiber. The elongation of carbon nanofiber bundles seemed to result from the continuous supply of nickel catalyst from the bamboo sprout-like shaped grains and carbon components from CH4 gas. Turn-on voltage of the field emission was measured around 0.8 V/mu m. Fowler-Nordheim plot of the measured values confirmed the field emission characteristic of the measured current. (c) 2005 Elsevier B.V. All rights reserved.