Controlled synthesis of single-walled carbon nanotubes by floating catalyst CVD for transparent conducting films: A critical role of loops

Single-walled carbon nanotubes (SWCNTs) are ideal candidates for transparent conductive films (TCFs) due to their excellent optical transparency and electrical conductivity. The geometry of SWCNTs, including the tube diameter, bundle length and bundle diameter, is vital to high-performance TCFs. Herein, we synthesized SWCNTs by floating catalyst chemical vapor deposition (FCCVD). The SWCNT geometries were tuned by hydrogen (H2), and we found that the tube diameter, bundle length and bundle diameter increase with the H2 concentration. Besides, we observed the formation of SWCNT loop at the tube ends. Both the number and circumference of loops increased with the increment of bundle length. Further, the loops were also found to affect the conductivity of SWCNT thin film. Excessive number of loops with large size could reduce the conductivity of SWCNT thin film. At the optimized H2 concentration, we obtained the SWCNT TCF with sheet resistances of 290 and 95 Ω/sq. for the pristine and AuCl3 doped SWCNT films, respectively, at 90% transmittance. Our work demonstrates the importance of H2 for SWCNT synthesis and the critical role of loops on film conductivity, blazing new ideas for future research to obtain SWCNT TCFs with improved performance.