Effects of Water Vapor on Diameter Distribution of SWNTs Grown over Fe/MgO-Based Catalysts

Abstract

With an interest in the H2O-assisted chemical vapor deposition (CVD) process, roles of H2O in tuning the diameter and chirality distributions of single-walled carbon nanotubes (SWNTs) were studied using Fe/MgO-based catalysts. A controlled amount of H2O was found to narrow the diameter distribution of SWNTs by reducing the populations of small- and large-diameter nanotubes. The addition timing of H2O vapor was investigated to understand the interaction between H2O and growing nanotubes or catalyst nanoparticles. Also, the addition of a small amount of Mo in the Fe/MgO catalyst was observed to reduce the diameter distribution of SWNTs, and H2O further promoted the formation of smaller-diameter SWNTs over the Fe−Mo/MgO catalyst. These results elucidate that the surface chemistry of catalyst nanoparticles exerted significant effects on the behaviors of H2O in the CVD process. Consequently, it is proposed that H2O first reacts with the surface of catalyst nanoparticle, and successively plays two aspects of ro...