Growth window and possible mechanism of millimeter-thick single-walled carbon nanotube forests

TL;DR

This study investigates the growth conditions and mechanisms for millimeter-thick single-walled carbon nanotube forests, emphasizing catalyst support effects and optimal reactant gas parameters for rapid, high-quality growth.

Contribution

It provides a detailed parametric analysis of growth conditions, revealing the role of Al2O3 support and reactant gas ratios in optimizing SWNT forest growth.

Findings

Al2O3 support enhances Fe catalyst activity.

Optimal H2O and H2 levels increase growth rate, excess degrades quality.

Narrow growth window identified for rapid SWNT growth.

Abstract

Our group recently reproduced the water-assisted growth method, so-called "super growth", of millimeter-thick single-walled carbon nanotube (SWNT) forests by using C2H4/ H2/ H2O/ Ar reactant gas and Fe/ Al2O3 catalyst. In this current work, a parametric study was carried out on both reaction and catalyst conditions. Results revealed that a thin Fe catalyst layer (about 0.5 nm) yielded rapid growth of SWNTs only when supported on Al2O3, and that Al2O3 support enhanced the activity of Fe, Co, and Ni catalysts. The growth window for the rapid SWNT growth was narrow, however. Optimum amount of added H2O increased the SWNT growth rate but further addition of H2O degraded both the SWNT growth rate and quality. Addition of H2 was also essential for rapid SWNT growth, but again, further addition decreased both the SWNT growth rate and quality. Because Al2O3 catalyzes hydrocarbon reforming, Al2O3 support possibly enhances the SWNT growth rate by supplying the carbon source to the catalyst nanoparticles. The origin of the narrow window for rapid SWNT growth will also be discussed.