Synthesis of Wafer-Scale SWCNT Forests with Remarkably Invariant Structural Properties in a Bulk-Diffusion-Controlled Kinetic Regime
Authors: Park Sei Jin , Moyer-Vanderburgh Kathleen , Buchsbaum Steven F. , Meshot Eric , Jue Melinda L. , Wu Kuang Jen , Fornasiero Francesco 
Published: August 2024

Robust synthesis of vertically aligned carbon nanotubes (VACNT) at large scale is required to accelerate deployment of numerous cutting-edge devices to emerging commercial applications.1 Large-area single-walled (SW) CNT forests with high densities and small diameters are especially important for many applications, yet they are conspicuously absent from the literature due to reproducibility and synthesis challenges, which are further exacerbated when flexible metal foils are used as support instead of traditional Si or quartz wafers. To address this need, we demonstrate that the structural characteristics of SWCNTs produced in a growth regime dominated by bulk diffusion of the gaseous carbon precursor are remarkably invariant over a broad range of process conditions (precursor concentration increased up to 30-fold, catalyst substrate area from 1 cm2 to 180 cm2, growth pressure from 20 to 790 mbar, and gas flowrates up to 8-fold).2 Forests structural properties are also preserved when growth is transitioned from Si wafers to Inconel metal foils.3 We show that a simple growth kinetics model that accounts for both reactant bulk diffusion and competing byproduct formation in the presence of excess hydrogen quantitatively reproduces the experimental data in the entire isothermal parameter space. The model enables critical predictions for process scale-up optimization including a potential 6-fold increase in CNT production rate, a ~ 90% carbon conversion efficiency in select conditions, and elimination of reaction rate decay observed at high pressures by using a hydrogen-free growth environment. This model-guided opportunity to substantially improve synthesis throughput and efficiency, in conjunction with the remarkably invariant CNT properties on both metal and insulating substrates, is appealing for reliable VACNT device fabrication at both small and industrial scales.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

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