Purification, structural evolutions, and electrical properties of carbon nanotube yarns processed via incandescent annealing

Abstract

Incandescent annealing in high vacuum is investigated for the purification of carbon nanotube (CNT) yarns produced via the floating catalyst chemical vapor deposition (CVD) method. The existing chemical purification routes damage CNTs and often require CNT dispersion. As an alternative, thermal annealing in inert or vacuum atmospheres has proved to remove impurities alongside improving CNT graphitization. Current-induced incandescent annealing process (IAP) in high vacuum provides a scalable and efficient route for the purification of CNT structures in a matter of seconds compared to hours of thermal annealing, reducing time and energy by orders of magnitude. In this study, electrical properties of CNT yarns are correlated with the morphological changes of their structure resulted from the IAP. Three distinct resistivity ranges based on the IAP current were identified and the detailed chemical composition, structure, and temperature-dependent resistivity of their corresponding yarns were investigated. It is concluded that the transport mechanism in the CNT yarns changes dynamically and drastically with the removal of amorphous carbon, iron, sulfur, and reduction in chlorine content. The correlations between the chemical composition, structure, and resistivity of samples provide new insight into CNT doping mechanisms and can be utilized to improve the conductivity of commercially available CNT yarns.