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

Abstract

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/H2 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.

Processing Methods Used in the Fabrication of Macrostructures Containing 1D Carbon Nanomaterials for Catalysis

“…The introduction of oxygen-containing functionalities has been demonstrated in carbon nanofibers, and their effect on their activity as catalyst or as catalyst support has been tested in several reactions, including ozonation [24] and catalytic wet air oxidation [25] of water contaminants, in fuel cell electrodes [26,27], nitrate [28], nitrobenzene [29,30], naphthalene [31], cinnamaldehyde [32,33], phenylacetylene [34] hydrogenation, nitrous oxide reduction [35], electrocatalytic oxygen reduction [35], methanol oxidation [36], Fischer-Tropsch reaction [27], and others [5]. Similar studies have been carried out when using other elements as dopants, such as nitrogen [37][38][39][40][41][42][43][44][45][46][47], boron [38,45,48], potassium [27,38,49], fluorine [50,51], phosphorous [45], or sulfur [52][53][54]. Nevertheless, the various morphologies of the 1D carbon nanofibers illustrated in Figure 2 may offer particular characteristics of interest to specific catalytic applications, in particular the potential presence of a large number of defects on the carbon lattice of the carbon nanofibers when compared with carbon nanotubes (Figure…”

Versatile Carbon Nanofiber-Based Sensors

“…This method is performed at a lower temperature than the normal CVD method. The collision of a gas-phase molecule with electrons facilitates the gas molecules’ decomposition, excitation, compounding, and ionization, thereby producing high-activity chemical groups. − Saidin et al synthesized CNFs utilizing the plasma-enhanced CVD (PECVD) method by employing a Ni/Cr-glass thin film catalyst for CNF growth. The influence of the different thicknesses of catalyst and acetylene to gaseous ammonia ratios were investigated, and they concluded that the optimum condition for the synthesis of CNFs is a 1:3 acetylene to NH 3 gas ratio with the width of 15 nm for the Ni/Cr-catalyst.…”

“…Shoukat and Khan synthesized vertically aligned CNFs by inductively coupled plasma-enhanced CVD using a temperature of ∼650 °C and toluene as a carbon source. Gupta and Sharma studied the effect of N doping on CNF growth by plasma-enhanced CVD and determined that N-doped CNFs had a lower tip diameter, smaller height, and improved field emission characteristics compared to undoped CNFs. Low substrate temperature and high deposition rates are required in this method …”

Carbon Nanofiber-Based Functional Nanomaterials for Sensor Applications

“…The plasma contains a large amount of high-energy electrons that can provide the activation energy required for the chemical vapor deposition process. The collision of electrons with gas phase molecules can promote the decomposition, compounding, excitation, and ionization processes of gas molecules, and generate various chemical groups with high activity [35,36,37]. While the plasma enhanced chemical vapor deposition method can produce aligned CNFs, the cost of this method is high, the production efficiency is low, and the process is difficult to control.…”