Influence of ethylene thermal decomposition on carbon nanotube growth: insights from a two-zone reactor study

초록

Gas-phase decomposition of the carbon precursor is a critical yet not fully understood step in the catalytic chemical vapor deposition growth of carbon nanotubes (CNTs). Here, we present a systematic investigation of how the thermal decomposition of C2H4 influences CNT growth. Using a custom-designed two-zone reactor with independently controlled preheating (decomposition) and CNT growth zones, we decoupled the effects of gas-phase decomposition from the growth temperature. Standard synthesis conditions were first established using Bayesian optimization, with the CNT growth zone temperature (Tg) fixed at 700 degrees C. CNTs were then synthesized at preheating zone temperatures (Tp) of 500, 600, 700, 800, and 900 degrees C while maintaining Tg at 700 degrees C under standard conditions. Carbon yield and IG/ID remained stable at 500, 600, and 700 degrees C but showed significant changes at 800 and 900 degrees C. To elucidate these variations, we analyzed the gas-phase composition at various temperatures using micro-GC. Significant changes in the gas-phase composition were observed above 700 degrees C, correlating with changes in carbon yield and crystallinity. Based on these results, we propose a mechanism by which differences in gas-phase chemistry lead to changes in the carbon yield and the IG/ID ratio. This study provides valuable insight into the role of gas-phase decomposition in CNT growth and highlights the potential of tuning gas-phase chemistry for controlled growth of CNTs.

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