A plasma-enhanced chemical-vapor deposition process was employed to synthesize carbon nanofibers (CNFs) on glass substrates patterned with Ni catalytic films. At the gas pressure of 20 mTorr and the substrate temperature (surface) of similar to 500 degrees C, the isolated and vertically aligned carbon nanofibers have been successfully synthesized. This paper reports experimental investigation of plasma properties characterized by the optical emission spectroscopy of the spectral line intensities of the various species such as hydrogen, C-2, and CH, as well as the rf characteristics at the biased substrate stage measured by an impedance meter. The measurement results reveal that the C-2 density increases with the acetylene/hydrogen flow ratio and the inductively coupled plasma (ICP) source power, as expected. The atomic hydrogen density, however, decreases with the flow ratio but increases with the ICP power. The resulting growth rate of CNFs increases with the C-2 density if atomic hydrogen density also increases accordingly, e.g., as the ICP power increases. The trend is reversed if the atomic hydrogen density decreases, due to too much amorphous carbon (a-C) layer formed as a result of oversupply of carbon but not enough atomic hydrogen to remove a-C. The experimental results also show that the etch effect upon the effective removing of the a-C on the surface of catalytic nanoparticles is further enhanced by ion bombardment, e.g., when either the flux (or current) or energy of the ions incident on the substrate surface increases, to give rise to an increase in growth rate. In our ICP reactor, the ion current increases with the ICP power, but it changes little when the bias power is varied. The ion energy increases with the bias power, but it decreases as the ICP power increases while the bias power is fixed. The latter one is because the plasma density increases with the inductively coupled plasma power. (c) 2006 American Vacuum Society.