Non-isothermal Chemical Vapor Deposition for Increasing Carbon Nanotube Yield

Increasing the yield of single-walled carbon nanotubes (CNTs) during growth is critical to their use in widespread applications. Here, we show that we can increase the CNT yield significantly by using a simple non-isothermal, continuous cooling procedure during CNT growth. While our typical isothermal growth conditions produce sparse bundled mats, our non-isothermal growth protocol results in high-density tall forests without the need for growth promoters, additional source materials, or additional processing. In situ experiments revealed that cooling rate and temperature difference are critical and were optimized for the highest increase in CNT yield. Moreover, the general applicability of the process was demonstrated by performing chemical vapor deposition growth experiments in a tube furnace on a variety of catalyst compositions and thicknesses. The observed improvement in the non-isothermal process across all experimental platforms and catalysts occurs due to a decline in particle coarsening and to the formation of smaller particles with an order of magnitude higher density compared to isothermal growth. We 1 attribute this to the de-stabilization of the catalyst films during continuous cooling. Non- isothermal growth provides a path forward for improving SWCNT yields while retaining all other growth conditions.