Correlation between the Carbon Nanotube Growth Rate and Byproducts in Antenna‐Type Remote Plasma Chemical Vapor Deposition Observed by Vacuum Ultraviolet Absorption Spectroscopy

Abstract For sp² or sp³ carbon material growth, it is important to investigate the precursors or intermediates just before growth. In this study, the density of ethylene (C₂H₄) outside the plasma discharge space and just before reaching the carbon nanotube (CNT) growth region is investigated by vacuum ultraviolet absorption spectroscopy for plasma discharge in an antenna‐type remote plasma chemical vapor deposition with a CH₄/H₂ system, with which the growth of very long (≈0.5 cm) CNT forests is achieved. Single‐wall CNT forests have the potential for application as electrodes in battery cells, vertical wiring for high current applications, and thermal interface materials. It is observed that the plasma discharge decomposes the CH₄ source gas and forms C₂H_x species, which reversibly reform to C₂H₄ in the plasma‐off state. In addition, the density of the formed C₂H₄ has a strong correlation to the CNT growth rate. Therefore, the C₂H₄ density is a good indicator of the density of C₂H_x species for CNT growth in the CH₄/H₂ plasma system.