October 26, 2022 Review by Mila Perera
Lawrence Livermore National Laboratory (LLNL) researchers are expanding the creation of vertically aligned single-walled carbon nanotubes (SWCNTs) that could transform a variety of commercial products ranging from auto parts, rechargeable batteries and sporting goods to water filters and boat hulls.
Vertically aligned carbon nanotubes growing from catalytic nanoparticles (gold color) on a silicon wafer on top of a heating stage (red glow). Diffusion of acetylene (black molecules) through the gas phase to the catalytic sites determines the growth rate in a cold wall shower reactor. Image credit: Adam Samuel Connell/LLNL
The study has been published in the journal Carbon.
The majority of CNT production currently is used in thin films and bulk composite materials, which rely on disordered CNT architectures. For various uses, organized CNT architectures, such as vertically aligned forests, offer significant advantages for utilizing the properties of separate CNTs in macroscopic systems.
Robust large-scale synthesis of vertically aligned carbon nanotubes is required to accelerate the deployment of numerous cutting-edge devices to emerging commercial applications.
Francesco Fornasiero, lead author and study scientist, Lawrence Livermore National Laboratory
Fornasiero added: “To address this need, we demonstrated that the structural features of single-walled CNTs produced at the wafer scale in a growth regime dominated by bulk diffusion of the gaseous carbon precursor are remarkably invariant over a wide range of process conditions”.
The researchers found that vertically oriented SWCNTs maintained high quality when the concentration of the precursor (the initial carbon) was increased 30-fold. In addition, the catalyst substrate area increased from 1 cm2 to 180 cm2. In addition, the gas flow was multiplied by 8 and the pressure grew from 20 to 790 Mbar.
The LLNL researchers presented a kinetics model showing that growth kinetics could be accelerated by using a lighter bath gas to support precursor diffusion. Furthermore, it illustrated that by-product formation becomes increasingly significant at higher growth pressure. This could be greatly facilitated by using a hydrogen-free growth environment.
The model also shows that the proper choice of the CNT growth recipe and fluid dynamics conditions can increase the production yield by 6 times and the carbon conversion efficiency to more than 90%.
These model projections, together with the remarkably preserved structure of CNT forests over a wide range of synthesis conditions, suggest that a bulk diffusion-limited growth regime may facilitate the preservation of vertically aligned CNT-based device performance over the scale
Jin Park, first author and study scientist, Lawrence Livermore National Laboratory
The researchers concluded that operation in a growth regime that a simple model of CNT growth kinetics quantitatively explains can aid process optimization and lead to faster deployment of cutting-edge vertically aligned CNT applications.
Applications include water purification, lithium-ion batteries, thermal interfaces, breathable fabrics, sensors and supercapacitors.
The other LLNL study authors are Kathleen Moyer-Vanderburgh, Steven Buchsbaum, Eric Meshot, Melinda Jue and Kuang Jen Wu. The work has had financial support from the Department of Biological and Chemical Technologies of the Defense Threat Reduction Agency.
Journal reference
Park, SJ, et al. (2022) Wafer-scale synthesis of SWCNT forests with remarkably invariant structural properties in a bulk diffusion-controlled kinetic regime. carbon
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