Growth of well-aligned carbon nanotube structures in successive layers

Layered structures of well-aligned carbon nanotubes were grown using three variations of vapor-phase chemical vapor deposition growth processes. The reactants (typically ferrocene and benzene) were introduced either directly to a heated furnace or carried into the furnace by evaporation or spray pyrolysis in an argon flow. Thick mats of densely packed, well-aligned nanotubes were produced when the reactants were continuously introduced to the reaction; however, when the reactant flow was interrupted, the pauses allowed growth to stop and then restart as a new layer. These pauses were achieved by either completely stopping the reactant flow for a given time or by modifying the dispensing system to introduce the reactants in discrete drops. Time intervals between drops were varied between 20 s and 120 s, with distinct layers observed for pauses of 30 s or greater. The best results were achieved when drops of a catalyst-rich solution were alternated with drops of pure benzene. Layers were grown with thicknesses ranging from several microns to several hundred microns, and structures were grown with well over 100 layers.