CO2-assisted growth of millimeter-tall single-wall carbon nanotube arrays and its advantage against H2O for large-scale and uniform synthesis

The CO2-assisted chemical vapor deposition (CVD) is reported as a versatile method for millimeter-tall vertically-aligned single-wall carbon nanotube (VA-SWCNT) arrays when compared with the famous H2O-assisted one. The mild oxidant CO2 enabled the VA-SWCNT growth with mostly equivalent structures and yield when it was added at a much higher concentration (0.3-1 vol%) than H2O (50 ppmv). Furthermore, CO2 showed a clear advantage for the uniform growth when 18 substrates (10 x 10 mm(2)) were loaded in one batch. The areal yield of VA-SWCNTs decreased drastically from 1.6 to 0.4 mg cm(-2) for the first 4 substrates with 50 ppmv H2O because of its depletion whereas it decreased more mildly from 1.6 to 0.8 mg cm(-2) for the whole 18 substrates with 1.0 vol% CO2. The gradual decrease in the SWCNT yield with 1.0 vol% CO2 was caused by the change in the carbon source depending on its position. The mixed feed of 0.30 vol% C2H2 (being converted to SWCNTs gradually) and 3.0 vol% C2H4 (yielding C2H2 gradually) realizes the uniform growth of VA-SWCNTs for the whole 18 substrates. The CO2-assisted CVD with optimized carbon feed is promising for the uniform growth of millimeter-tall SWCNTs in large areas. (C) 2018 The Authors. Published by Elsevier Ltd.