Rapid Characterisation of Millimetre-Tall Vertically Aligned Carbon Nanotube Arrays: Growth Optimisation by Tuning the Catalyst Film Thickness

This study aims to establish a quick and sustainable approach for optimising the growth of millimetre-tall vertically aligned carbon nanotube (VACNT) arrays through simple catalyst tuning. To achieve this swiftly, a rapid and handy characterisation protocol is essential. Herein, we propose and validate such a method for the rapid characterisation of VACNTs, which concurrently improves upon the traditional weight-gain density calculation for VACNT arrays. We demonstrate the efficacy of this combined strategy by systematically investigating the influence of iron (Fe) catalyst film thickness (0.8-2.0 nm) on the microstructure and density of VACNT arrays synthesised via thermal chemical vapour deposition (TCVD). Catalyst morphology was characterised by atomic force microscopy (AFM), while transmission electron microscopy (TEM) provided nanotube diameter and wall-number distributions. Scanning electron microscopy (SEM) measured array height for areal density estimation, with Fourier component analysis of SEM cross-sections applied to correct height underestimations from tube tortuosity. It was observed that increasing Fe thickness enlarges and broadens catalyst particle distributions, enabling modest tuning of VACNT dimensions without compromising packing density. An optimum film thickness of similar to 1.1 nm was identified, maximising areal density at similar to 2 x 10(10) CNTs cm(-2). The integrated imaging and analysis approach presented here offers a practical and efficient pathway for rapid VACNT microstructure control and density assessment, facilitating future optimisation cycles. Furthermore, a transition in growth mode was observed, which further confirms the decisive role of the catalyst film thickness.