Mechanism of polymer removal from semiconducting single-walled carbon nanotubes via rapid thermal processing: insights from in situ environmental transmission electron microscopy

Abstract

Semiconducting single-walled carbon nanotubes (s-SWCNTs), sorted using conjugate polymers like poly[9-(1-octylonoyl)-9H-carbazole-2,7-diyl] (PCz), are crucial for high-performance nanoelectronics. However, residual PCz may hinder device performance, for instance, by degrading carrier efficiency at the CNT–metal contacts and impairing gate control at CNT–dielectric interfaces. Effective removal of this polymer without introducing significant damage to the carbon nanotubes is essential for optimal performance. In this work, we developed and optimized a two-step (N₂/O₂) rapid thermal processing (RTP) method, involving heating at 600 °C in N₂ for 4 minutes followed by 400 °C in O₂ for 6 minutes, achieving effective PCz removal. The removal efficiency and potential defect introduction were monitored using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Furthermore, in situ environmental transmission electron microscopy (ETEM) provided direct insight into the removal mechanism: initial side chain degradation occurs in the inert atmosphere, potentially driven by thermal expansion differences, followed by backbone degradation in the O₂ atmosphere. Optimal processing conditions determined through combined electrical transport measurements and TEM analysis resulted in improved CNT field effect transistor (FET) performance, including reduced contact resistance. This study provides crucial mechanistic insights into polymer removal, paving the way for enhanced s-SWCNT-based nanoelectronics devices.