Vertically aligned carbon nanotubes (CNTs) with long length and high density were successfully synthesized on SiO2, Ta, and Ti substrates by thermal chemical vapor deposition (CVD) The use of Fe catalyst film supported by an Al buffer layer (Fe/Al) has a significant influence on the increase of the number density of the aligned CNTs and the decrease of their diameter. The time dependencies of the aligned CNTs growth show that there is a limit to the length of the aligned CNTs formation. The aligned CNTs can be lengthened further using an intermittent growth method. These findings for the aligned CNTs synthesized on SiO2, Ta, and Ti substrates demonstrate that the thermal intermittent CVD with a Fe/Al multilayer is a versatile method for obtaining vertically aligned CNTs with moderate length, for use in various device applications. (c) 2005 American Vacuum Society.