Understanding Single-Walled Carbon Nanotube Growth for Chirality Controllable Synthesis

Chirality defines the structural and electronic properties of a single-walled carbon nanotube (SWCNT), and therefore, synthesizing SWCNT samples with single chirality is essential for future high-end applications, such as replacing silicon in next-generation electronics. Since its discovery in 1991, to realize the selective growth of SWCNTs with a unique structure has been a key focus of SWCNT research. Chirality is currently understood to be assigned at birth and might be changed during the growth process. Understanding the mechanism of chirality assignment during nucleation and chirality-dependent growth kinetics is essential for realizing the final goal of SWCNT synthesis, i.e., the large-scale synthesis of SWCNTs with a specific chiral index. From 2003, we have systematically explored chirality assignment during SWCNT nucleation, how the chirality of a SWCNT affects its growth, and how the chirality changes during growth. Together with our experimental collaborators, we have realized the chirality-specific growth of SWCNTs via a few designed experimental routes. In this account, we will review all these studies and present our perspectives on this very important research topic. We will first introduce the screw dislocation theory of SWCNT growth to elucidate how the chirality affects the growth rate of a SWCNT and the abundance of each SWCNT in the final product. Second, a modified screw dislocation theory, which describes the SWCNT???s growth kinetics on a solid catalyst and its impact on chirality control during synthesis is presented. Third, the random chiral angle assignment during SWCNT nucleation on liquid catalysts is discussed as well as why chirality control in SWCNT growth is so challenging. Together with previous experimental reports, we further demonstrate that solid catalysts have a great advantage in realizing chirality-selective SWCNT growth. Based on our current understanding, we propose three strategies to realize chirality-selective SWCNT growth, (i) controlling the symmetry of solid catalyst particles, (ii) varying the growth conditions, and (iii) controlling the feedstock and etching agent during growth. We expect this account will give the reader a comprehensive understanding of the mechanism behind SWCNT growth and motivate further studies on selective growth to achieve the best performance of SWCNT-based devices in the future