Tailoring the Morphology of Vertically Aligned Carbon Nanorod Arrays Grown on Co Catalyst Nanoparticles and using MW-PECVD

This study reports a direct approach to synthesizing vertically aligned carbon nanorod arrays (VA-CNRA) using microwave plasma-enhanced chemical vapor deposition (MW-PECVD) at 300 °C, on Cobalt (Co) catalyst nanoparticles grown by thermal annealing (750 °C) of 10 nm thick Co layer deposited by Radio frequency (RF) magnetron sputtering. To grow the VA-CNRA, the gas ratio in the plasma was optimized, focusing on the kinetics of the source gas dissociation and recombination. The reduced concentrations of acetylene (C2H2) impede the optimal alignment of CNRA in the absence of the steric hindrance, resulting in their horizontal growth along the direction of gas flow via the “kite-mechanism”. However, at a higher gas flow ratio, the attractive van der Waals potential among the CNRs was anticipated to induce aggregation when they arrive in proximity and vertical growth alignment of the nanorods via the higher deposition rates. Carbon nanorod films were analyzed using various spectroscopic techniques to understand the growth orientations, which suggests that the carbon nanorods were formed via the base-growth mechanism. Nano flower-like VA-CNRA were formed at higher C2H2/H2 ratios. Notably, a distinct flower-like structure with whisker-like nanostructure petals was formed at a C2H2/H2 flow ratio of ∼0.57. Compared to other nanorod structures, VA-CNRA, grown at optimal gas ratio, exhibited superior crystalline graphite, with 76% sp2 C=C bonding along with a maximum of I2D/IG, and a minimum of ID/IG intensity ratio in the Raman data. High-resolution TEM confirmed robust growth of CNRs, with an average diameter of ∼370 ±3 nm. This innovative method enables large-scale production of VA-CNRA with high surface areas for energy applications.