Vertically aligned carbon nanotubes (VACNTs) of increased length are produced in a method that introduces ferrocene into an acetylene/hydrogen/inert gas stream during a chemical vapor deposition process. The ferrocene is supplied from a controllable thermal sublimation source. Independent and precise control of the ferrocene into the feedstock gas facilitates the growth of thick films comprising long carbon nanotubes on conductive substrates. An order of magnitude increase in the length of CNTs, from a few hundred microns to several mm is achieved.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
 The United States Government has rights in this invention pursuant to Contract No. DE-AC05-00OR22725 between the United States Department of Energy and UT-Battelle, LLC.