Modelling the effects of nitrogen doping on the carbon nanofiber growth via catalytic plasma-enhanced chemical vapour deposition process

An analytical model is developed to describe the effects of nitrogen doping on the growth of the carbon nanofibers (CNFs) and to elucidate the growth mechanism of nitrogen-contained carbon nanofibers (N-CNFs) on the catalyst substrate surface through the plasma-enhanced chemical vapour deposition (PECVD) process. The analytical model accounts for the charging of CNFs, kinetics of all plasma species (electrons, ions, and neutrals) in the reactive plasma, generation of carbon species on the catalyst nanoparticle surface due to dissociation of hydrocarbons, CNF growth due to diffusion and precipitation of carbon species, and various other processes. First-order differential equations have been solved for glow discharge plasma parameters for undoped CNFs (CNF growth in C2H2/H-2 plasma) and nitrogen-doped CNFs (N-CNF growth in C2H2/NH3 plasma). Our investigation found that nitrogen-doped CNFs exhibit lower tip diameters and smaller heights compared to the undoped CNFs. In addition, we have estimated that nitrogen-doped CNFs have more enhanced field emission characteristics than the undoped CNFs. Moreover, we have also observed that N-CNFs' growth rate increases and tip diameter decreases as the C2H2/NH3 gas ratio decreases. The theoretical results of the present investigation are consistent with the existing experimental observations.