| 초록 |
The chirality of single-walled carbon nanotubes (SWCNTs) has great importance since their physical and electronic properties strongly depend on it. However, the chirality of irregular structures of SWCNTs, especially, those formed during the growth process, was difficult to define in contrast to the definition of the chirality of ideal SWCNTs, usually done using a graphene sheet with the direction of roll-up vector. We have developed a robust theoretical method for the determination of the local chirality based on individual hexagons that compose SWCNTs. The method and code have been applied to various SWCNT-like irregular structures that are formed during the growth process. The local chiral index (LOCI) and its distribution are well-defined for irregular structures as well as ideal structures of SWCNTs, and can be used to characterize any SWCNT-like irregular structures in terms of local chirality. We applied LOCI method to the growth of (5,5) and (8,0) SWCNTs simulated using quantum chemical molecular dynamics (QM/MD). For both armchair (5,5) and zigzag (8,0) SWCNTs, QM/MD simulations indicate that defect healing - the process of defect removal during growth - is a necessary, but not sufficient condition for chirality-controlled SWCNT growth. Time-evolution (TE-)LOCI analysis shows that healing, while restoring the pristine hexagon structure of the growing SWCNT, also leads to changes in the local chirality of the SWCNT edge region and thus of the entire SWCNT itself. In this respect, we show that zigzag SWCNTs are significantly inferior in maintaining their chirality during growth compared to armchair SWCNTs. The recent results of QM/MD simulations for the chirality-controlled SWCNT growth are also discussed. |
