Towards the synthesis of semiconducting single-walled carbon nanotubes by floating-catalyst chemical vapor deposition: Challenges of reproducibility

High-purity semiconducting single-walled carbon nanotubes (s-SWCNTs) are of paramount significance for the fabrication of high-performance electronics. Here, we present continuous production of highpurity, long, and isolated s-SWCNTs by gas-phase synthesis, retaining the pristine morphologies of assynthesized nanotubes. The s-SWCNTs were synthesized at ca. 920 degrees C using ethanol and methanol as carbon source and growth enhancer, respectively in N2 and H2. The purity of as-produced s-SWCNTs with a mean length of 15.2 mm can reach 98% as determined by optical absorption spectroscopy. We observed that the overpressure in the reactor and methanol are the principal causes of the enrichment of sSWCNTs. Specifically, the s-SWCNTs were found to be more negatively charged, and oxygen-contained species play critical roles in the s-SWCNT synthesis. Through the demonstration of field-effect transistors, the s-SWCNTs exhibit a high mean charge carrier mobility of 453.3 cm2 V-1 s-1 which is 2.27 times higher than that of the transistors fabricated with high-quality dispersion-processed SWCNTs. Additionally, we discuss the challenges of synthesis repeatability and recommend a few tips to improve reproducibility. Our study represents an important step towards the scalable production of clean, long, and isolated s-SWCNTs with high purity and narrow bandgap distribution.(c) 2022 The Author(s). Published by Elsevier Ltd.

Automated summary

In this study, high-purity, long, and isolated s-SWCNTs were continuously produced by gas-phase synthesis, maintaining their pristine morphologies. The as-produced s-SWCNTs had a purity of 98% and a mean length of 15.2 mm. The enrichment of s-SWCNTs was found to be mainly caused by overpressure in the reactor and methanol, and the s-SWCNTs exhibited a higher negative charge and a critical role of oxygen-contained species in their synthesis. The field-effect transistors based on s-SWCNTs showed a high mean charge carrier mobility, which was 2.27 times higher than that of transistors fabricated with dispersion-processed SWCNTs. The challenges of synthesis repeatability were discussed, and recommendations for improving reproducibility were provided. This study is an important step towards the scalable production of clean, long, and isolated s-SWCNTs with high purity and narrow bandgap distribution.