Optimization of the chemical vapor deposition process for carbon nanotubes fabrication

A coupled boundary-layer laminar-flow hydrodynamic, heat-transfer, gas-phase chemistry and surface chemistry model is developed to analyze, at the reactor length-scale, chemical vapor deposition (CVD) of carbon nanotubes from a gas mixture consisting of methane (carbon precursor) and hydrogen (carrier gas) in the presence of cobalt catalytic particles in a cylindrical reactor. The model allows determination of the gas-phase fields for temperature, velocity, and species concentration as well as the surface species coverages, the carbon nanotubes growth rate and the deposition rate of amorphous carbon. Experimentally determined carbon deposition rates and carbon nanotubes growth rates at different processing conditions are used to validate the model. The model is also coupled with the Genetic Algorithm to determine the process parameters (the gas temperature and velocity at the reactor inlet, the reactor-wall temperature, the pressure, and the mole fraction of methane in the gas mixture) which maximize the carbon nanotubes yield while minimizing the amount of deposited amorphous carbon.