Iridium‐Catalyzed Single‐Walled Carbon Nanotube Synthesis by Alcohol‐Gas‐Source Method Under Low Ethanol Pressure: Growth Temperature Dependence

Abstract Single‐walled carbon nanotubes (SWCNTs) are grown via an Ir‐catalyzed gas‐source‐type cold‐wall chemical vapor deposition (CVD) method under high vacuum. A nozzle injector is used to supply ethanol gas. The grown SWCNT surface shows a colored concentric morphology. This corresponds to the in‐plane distribution of SWCNT lengths, which is induced by in‐plane variations in the ethanol pressure. Raman spectroscopy and scanning electron microscopy are used to investigate the dependence of the SWCNT yield on the growth temperature and ethanol pressure. The ethanol pressure that gives the highest SWCNT yield decreases with decreasing growth temperature. Optimization of the ethanol pressure enables SWCNT growth between 500 °C and 800 °C, and vertically aligned SWCNTs are grown at 700 °C and 800 °C. The SWCNT diameters are small at all growth temperatures, namely less than 0.9 nm for growth at 500 °C and 600 °C, and less than 1.0 nm for growth at 700 °C and 800 °C. The estimated activation energy for SWCNT growth with an Ir catalyst is 0.97 eV, which is much smaller than that with a Co catalyst.