Abstract
Carbon Nanotube (CNT) arrays and graphene have undergone several investigations to achieve efficient field emission (FE) owing to CNT’s remarkable large aspect ratio and graphene’s exceptional FE stability. However, when dense CNT arrays and planar graphene layers were used as field emitters, their field enhancement factor reduced dramatically. Therefore, in this paper, we numerically analyze the growth of a dense CNT array with planar graphene layers (PGLs) on top, resulting in a CNT-PGL hybrid and the associated field enhancement factor. The growth of the CNT array is investigated using Plasma Enhanced Chemical Vapor Deposition (PECVD) chamber in C2H2/NH3 environment with variable C2H2 flow, Ni catalyst film thickness, and substrate temperature followed by PGL precipitation on its top at an optimized cooling rate and Ni film thickness. The analytical model developed accounts for the number density of ions and neutrals, various surface elementary processes on catalyst film, CNT array growth, and PGLs precipitation. According to our investigation, the average growth rate of CNTs increases and then decreases with increasing C2H2 flow rate and catalyst film thickness. CNTs grow at a faster rate when the substrate temperature increases. Furthermore, as the chamber temperature is lowered from 750 °C to 250 °C in N2 environment and Ni film thickness grows, the number of the graphene layers increases. The field enhancement factors for the CNT array and hybrid are then calculated based on the optimal parameter values. The average height of the nanotubes, their spacing from one another, and the penetration of the electric field due to graphene coverage are considered while computing the field enhancement factor. It has been found that adding planar graphene layers to densely packed CNTs can raise its field enhancement factor. The results obtained match the current experimental observations quite well.
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