Modeling of the in-situ nitrogen (N) doping of graphene-carbon nanotube (CNT) hybrids in a plasma medium and their field emission properties

Abstract

A numerical formalism for investigating the effect of in-situ nitrogen doping (N-doping) on the plasma-assisted growth of graphene-carbon nanotube (CNT) hybrids is established. The formalism includes the energy balance on the catalyst particle and the kinetics of plasma species with contribution from hydrogen, hydrocarbon, and ammonia that aids in N-doping, for the growth of in-situ N-doped CNT, graphene, and graphene-CNT hybrids. The growth rate equations for the N-doped CNT, graphene, and graphene-CNT hybrids are also set up as a part of the model. With N-doping, the hydrogen ionic species density initially increases and then falls, promoting the growth of higher order hydrocarbons in plasma. The electron density also increases with N-doping such that the electron-mediated ionization and dissociation processes, increase eventually affecting the availability of growth precursors. The cumulative effect of the variation in the plasma species density with N-doping leads to the growth of nanostructures with a high aspect ratio. In the present work, the field enhancement factor (β) of the graphene-CNT hybrids is approximated as the ratio of its dimension along the y-axis to that along the z-axis. The β of graphene-CNT hybrids is found to be larger than that of the undoped and N-doped CNT and graphene. Moreover, N-doping further enhances the β of graphene-CNT hybrids.