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

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 C2Hx 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 C2Hx species for CNT growth in the CH4/H2 plasma system. The density of C2H4 just before reaching the carbon nanotube (CNT) growth region is investigated by vacuum ultraviolet absorption spectroscopy for an antenna‐type remote plasma chemical vapor deposition with a CH4/H2 system. The plasma discharge forms C2Hx species, which reversibly reform to C2H4 in the plasma‐off state. The density of formed C2H4 is correlated to the CNT growth rate.