3X TALLER CARPETS OF VERTICALLY ALIGNED CARBON NANOTUBES THROUGH DIFFERENTIAL PREHEATING OF HYDROCARBON DECOMPOSITION AND WATER FORMATION

It has been shown that preheating the incoming hydrocarbon precursors and of forming water vapor from oxygen and hydrogen can significantly affect the growth of vertically aligned carpets of carbon nanotubes (CNTs). In this study, we performed differential preheating of the incoming gases to decouple the water formation and the hydrocarbon decomposition processes. We revealed different process parameter sweet spots for water vapor formation (formed by reacting H₂ and O₂) and for hydrocarbon decomposition.

We used a sophisticated system of multi-zone thermal chemical vapor deposition (CVD) furnaces in parallel and in series to study the effects of thermal preheating of these precursors prior to their reaching the growth zone. We analyzed a dozen of possible preheating combinations and showed how an appropriate combination of gas residence times for both hydrocarbons and water formation can significantly increase CNT growth to exceed 3 mm in height. Extensive AFM, HRTEM and SEM characterizations of the CNTs indicate how preheating affects the CNT height, diameter, and crystallinity. This analysis helps to better understand the mechanisms at play for the precursor gases prior to reaching the sample and helps to design more efficient synthesis systems for CNT growth.