Carbon nanotubes were grown on Si substrates using a plasma enhanced chemical vapor deposition technique under various gaseous compositions, microwave powers, and pressures. An iron-containing compound was used as the catalyst. The hydrocarbon used was methane. The resulting carbon nanotubes were examined using scanning electron microscopy and transmission electron microscopy. The diameters of carbon nanotubes (CNTs) were found to be dominated by methane concentration and plasma power. It was also found that the catalyst particles were deformed during the growth of CNTs which led to a sheath growth mechanism. (C) 2003 Elsevier B.V. All rights reserved.