Catalyst-free low-temperature growth of carbon nanofibers by microwave plasma-enhanced CVD

Catalyst-free low-temperature growth of carbon nanofibers was performed by a microwave plasma-enhanced chemical vapor deposition using CO/Ar/O(2) system. At the optimum oxygen concentration of O(2)/CO = 7/1000, vertically aligned CNFs can be synthesized at temperature as low as 180 degrees C without any catalyst materials, whose diameter is about 50-100 nm and growth rate is about 5 nm/s. It is concluded that the addition of a small amount of O(2) is the key for the synthesis of CNFs without catalyst, because it suppresses the isotropic deposition of amorphous carbon and assists the anisotropic linear growth of crystallized carbon deposits. (C) 2009 Elsevier B.V. All rights reserved.