The role of surface species in chemical vapor deposited carbon nanotubes.

Chemical vapor deposition (CVD) of carbon nanotubes (CNTs) has been investigated using a coupled gas phase and surface chemistry model. This model successfully bridged the gap between the reactor and molecular length scales and allowed individual surface kinetic processes to be identified as growth limiting directly from reactor scale parameters. Carbon nanotube growth rate is a function of the reactor wall temperature such that deposition would occur in the transition region between the hydrogen abstraction and hydrocarbon adsorption limited regimes. Deposition was limited under low reactor temperatures or rich methane conditions by hydrogen abstraction from surface bound hydrocarbons due to the availability of gaseous H(1). At high reactor temperatures and rich hydrogen conditions, the deposition reaction was shown to be limited by hydrocarbon adsorption onto the nanoparticle surface. Optimal process conditions for efficient CNT production are discussed, as well as identifying the limiting reaction steps for the surface chemistry.