The Ostwald ripening behavior of Fe catalyst films deposited on thin alumina supporting layers is demonstrated as a function of thermal annealing in H2 and H2/H2O. The addition of H2O in super growth of single-walled carbon nanotube carpets is observed to inhibit Ostwald ripening due to the ability of oxygen and hydroxyl species to reduce diffusion rates of catalyst atoms. This work shows the impact of typical carpet growth environments on catalyst film evolution and the role Ostwald ripening may play in the termination of carpet growth.

Advances in the synthesis and scalable manufacturing of single-walled carbon nanotubes (SWCNTs) remain critical to realizing many important commercial applications. Here we review recent breakthroughs in the synthesis of SWCNTs and highlight key ongoing research areas and challenges. A few key applications that capitalize on the properties of SWCNTs are also reviewed with respect to the recent synthesis breakthroughs and ways in which synthesis science can enable advances in these applications. While the primary focus of this review is on the science framework of SWCNT growth, we draw connections to mechanisms underlying the synthesis of other 1D and 2D materials such as boron nitride nanotubes and graphene.

We have studied the lifetime, activity, and evolution of Fe catalysts supported on different types of alumina: (a) sputter deposited alumina films (sputtered/Fe), (b) electron-beam deposited alumina films (e-beam/Fe), (c) annealed e-beam deposited alumina films (annealed e-beam/Fe), (d) alumina films deposited by atomic layer deposition (ALD/Fe), and (e) c-cut sapphire (sapphire/Fe). We show that the catalytic behavior, Ostwald ripening, and subsurface diffusion rates of Fe catalyst supported on alumina during water-assisted growth or "supergrowth" of single-walled carbon nanotube (SWNT) carpets are strongly influenced by the porosity of the alumina support. The catalytic activity increases in the following order: sapphire/Fe < annealed e-beam/Fe < ALD/Fe < e-beam/Fe < sputtered/Fe. With a combination of microscopic and spectroscopic characterization, we further show that the Ostwald ripening rates of the catalysts and the porosity of the alumina support correlate with the lifetime and activity of the catalysts. Specifically, our results reveal that SWNT carpet growth is maximized by very low Ostwald ripening rates, mild subsurface diffusion rates, and high porosity, which is best achieved in the sputtered/Fe catalyst. These results not only emphasize the connection between catalytic activity and particle stability during growth, but guide current efforts aimed at rational design of catalysts for enhanced and controlled SWNT carpet growth.

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