Large Area, High-Density SWCNT Forests with Remarkably Invariant Structural Properties over a Wide Range of Synthesis Conditions

Abstract

Driven by the exceptional thermal, electrical, optical, mechanical and fluidic properties of single-walled carbon nanotubes (SWCNT), commercial use of vertically aligned “forests” are on the horizon for applications1 ranging from optical absorbers and thermal interfaces to selective membranes and advanced fabrics.2,3 Large-area SWCNT forests with high densities and small diameters are especially important for many applications, yet they are conspicuously absent from the literature due to synthesis challenges.Here, we demonstrate synthesis of high-density (> 1012 CNTs/cm2), small-diameter (~ 2 nm) SWCNT forests with structural characteristics that remain uniform over large areas (up to 6-in. diameter)4 and, surprisingly, largely unchanged over a wide range of synthesis conditions. We find also that our growth regime enables a record-high carbon conversion efficiency and a stable mass kinetics, both of which are invariant with catalyst type (Fe vs Fe/Mo mixes). To identify the limiting steps in the SWCNT growth kinetics and the factors contributing to the process robustness, we determine the dependence of the reaction rate and carbon conversion efficiency on broad ranges of synthesis parameters. Effects of catalyst area (from 1 × 1 cm2 to 6-in wafers), growth pressure (10-750 mbar), gas composition (30-fold acetylene partial pressure variation), and flowrates are presented.Our demonstration of such exceptionally robust and reproducible synthesis of high-density forests over large areas provides valuable insights for future scale-up efforts of SWCNT forest production that are necessary for widespread adoption of advanced CNT technologies. 1. R. Rao et al., ACS Nano., 12 (2018) 11756.2. N. Bui, E. R. Meshot, S. Kim, J. Peña, P. W. Gibson, K. J. Wu, F. Fornasiero, Adv. Mater., 28 (2016) 5871.3. Y. Li, C. Chen, E. R. Meshot, S. F. Buchsbaum, M. Herbert, R. Zhu, O. Kulikov, B McDonald, N. Bui, M. L. Jue, S. Park, C. Valdez, S. Hok, C. J. Doona, K. J. Wu, T. M. Swager, F. Fornasiero, submitted (2019)4. E. R. Meshot, S. Park, S. F. Buchsbaum, M. L. Jue, T. R. Kuykendall, E. Schaible, L. B. Bayu Aji, S. Kucheyev, K. J. Wu, F. Fornasiero, submitted (2019).This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-797268