Dopant-Inherent Mechanisms of Atmospheric Stability in Chemically N-Doped Semiconducting Carbon Nanotubes Revealed by Tracking Optical Absorption

The stability of n-type single-walled carbon nanotubes (CNTs) in air is crucial for the development of CNT-based electronics and energy-harvesting generators. Various attempts using chemical dopants have led to significant improvements in the air tolerance of n-type CNTs; however, our understanding of their stability depending on the CNTs' structural features and dopant species, particularly that of the air sensitivity of semiconducting CNTs, remains incomplete. In this study, we investigated the atmospheric stability of chemically n-doped CNTs using time-course infrared absorption spectroscopy. This technique is advantageous for selectively monitoring the stability of semiconducting CNTs by tracking changes in the excitonic absorption and plasmonic response. Furthermore, its adaptability was confirmed by examining the stability dependences on the average tube diameters. Based on this evaluation method, distinct stabilization mechanisms for doping CNTs using supramolecular salt-based dopants (e.g., crown ether complexes) and superelectron donors (SEDs; e.g., 4-(2,3-dihydro-1,3-dimethyl-1H-benzimidazol-2-yl)-N,N-dimethylbenzenamine) were examined. These findings can pave the way for the promising design of practical, flexible electronic devices and energy generators involving n-doped semiconducting CNTs.