Synthesis of carbon nanotubes on metal alloy substrates with voltage bias in methane inverse diffusion flames

Vertically well-aligned multi-walled carbon nanotubes (MWNTs) with uniform diameters (∼15 nm) were grown on catalytic probes at high yield rates in an inverse diffusion flame (IDF) of a co-flow jet configuration using methane as fuel. Varied parameters investigated included: alloy composition (e.g. Fe, Ni/Cu, Ni/Cr/Fe), sampling positions within the flame structure, and voltage bias applied to the probe substrate. Spontaneous Raman spectroscopy was utilized to determine the local gas-phase temperature, as well as the concentrations of carbon-based precursor species (e.g. CO, C2H2) within the flame structure at specific locations of carbon nanotube (CNT) growth during synthesis. The variation of the aforementioned parameters strongly affects CNT formation, diameter, growth rate, and morphology.