Roles of sulfur in floating-catalyst CVD growth of single-walled carbon nanotubes for transparent conductive film applications

Abstract

Sulfur is an effective promoter for growing single-walled carbon nanotubes (SWCNTs) and tuning their structural properties. In particular, sulfur has been utilized in the floating-catalyst chemical vapor deposition (FC-CVD) process to fabricate SWCNT-based transparent conductive films (TCFs). However, in-situ catalyst nucleation process in conventional FC-CVD, hinders to correlate the substantial role of sulfur in tuning SWCNTs synthesis and enhancing the performance of SWCNT-based TCFs. Herein, we have for the first time, systematically studied the roles of sulfur on yield, morphology, and structure of SWCNTs grown by FC-CVD, using ex-situ Fe and Co catalyst particles. We found that SWCNT yield is largely dependent on the amount of sulfur introduced into the FC-CVD reactor and on catalyst composition. More importantly, the addition of an optimized amount of sulfur resulted in a three-fold enhancement of the opto-electronic performance of SWCNT-TCFs, by increasing diameter and bundle length along with improving the quality of SWCNTs. Surprisingly, electron diffraction analysis revealed that SWCNTs grown from both Fe and Co display wide chirality distributions spanning from zig-zag to armchair edges, indicating that the sulfur promoter has little influence on the chirality modulating of SWCNTs.