The role of surface species in chemical vapor deposited carbon nanotubes

Abstract

Chemical vapor deposition (CVD) of carbon nanotubes (CNTs) has been investigated usinga coupled gas phase and surface chemistry model. This model successfully bridgedthe gap between the reactor and molecular length scales and allowed individualsurface kinetic processes to be identified as growth limiting directly from reactorscale parameters. Carbon nanotube growth rate is a function of the reactor walltemperature such that deposition would occur in the transition region between thehydrogen abstraction and hydrocarbon adsorption limited regimes. Deposition waslimited under low reactor temperatures or rich methane conditions by hydrogenabstraction from surface bound hydrocarbons due to the availability of gaseousH1. At high reactor temperatures and rich hydrogen conditions, the deposition reaction wasshown to be limited by hydrocarbon adsorption onto the nanoparticle surface. Optimalprocess conditions for efficient CNT production are discussed, as well as identifying thelimiting reaction steps for the surface chemistry.