EFFECT OF PLASMA ON THE GROWTH AND ELECTRONIC PROPERTIES OF CNT AND ITS HYBRID

Abstract

CNT-Graphene hybrids are three-dimensional, densely packed carbon atoms organized hexagonally in a three-dimensional lattice. Vertically aligned hybrids are promising candidates for applications such as field emission devices, electronic sensors, and electron emission displays. There are several ways available for synthesizing hybrids; however, plasma-based techniques, such as plasma enhanced chemical vapour deposition (PECVD), are only utilized to manufacture vertically oriented hybrids at low temperatures. The purpose of this thesis is to gain a thorough understanding of the hybrid's growth mechanism in a reactive plasma environment, as well as the field emission characteristics that result. In this paper, multiscale analytical models characterizing the growth mechanism of the CNT-graphene hybrid on the catalyst-substrate interface are created. The model for hybrid growth in plasma takes into account the hybrid's charging in the plasma, the particle and energy balance of the plasma species (charged and neutral), and the energy balance of the CNT and catalyst surface. For typical glow discharge plasma parameters, the model equations were solved simultaneously. Plasma parameters (number densities and temperatures of electrons and ions), as well as the presence of dopant species (nitrogen species), have been discovered to have a substantial impact on the hybrid's development characteristics and, as a result, its field emission properties. The multistage model for plasma-assisted catalyzed hybrid growth consists mostly of two sub-analytical models. The plasma sheath model accounts for the excitation of gaseous sources caused by applied plasma power and plasma species kinetics, whereas the surface deposition model incorporates the adsorption and dissociation of carbon bearing species over the catalyst nanoislands active surface (free surface available for plasma species adsorption) to generate building species (carbon species) through a variety of surface processes, including the diffusion of building species over the catalyst nanoislands' surface, the production of carbon clusters, the nucleation and growth of graphene islands, and the vertical growth of hybrids. The model equations were solved using experimentally determined initial conditions. Plasma parameters, doping elements (nitrogen), gas flow rate, catalyst layer vi thickness, substrate temperature, and cooling rate all have a significant impact on the hybrid's growth characteristics and, as a result, its field emission properties. Furthermore, it is assumed that graphene sheet formation over the CNT surface is defect guided, and that the density profiles of the defects formed over the CNT surface may be controlled by appropriately altering the plasma working parameters A thorough comparison of the acquired theoretical results to the available experimental observations verifies the current model's appropriateness. The current thesis work can be extended to build thin and long vertically oriented hybrids for prospective uses in field emitters, as the hybrid's field emission characteristics are determined by its geometrical properties, i.e., height and thickness. Furthermore, the current study might be extended to evaluate the formation of additional carbon-based nanostructures.