Molecular\nDynamics of Catalyst-Free Edge Elongation\nof Boron Nitride Nanotubes Coaxially Grown on Single-Walled Carbon\nNanotubes

Recent advances in\nlow-dimensional materials have enabled the synthesis\nof single-walled carbon nanotubes encapsulated in hexagonal boron\nnitride (BN) nanotubes (SWCNT@BNNT), creating one-dimensional van\nder Waals (vdW) heterostructures. However, controlling the quality\nand crystallinity of BNNT on the surface of SWCNTs using chemical\nvapor deposition (CVD) remains a challenge. To better understand the\ngrowth mechanism of the BNNT in SWCNT@BNNT, we conducted molecular\ndynamics (MD) simulations using empirical potentials. The simulation\nresults suggest that spontaneous BN nucleation is unlikely to occur\non the outer surface of the SWCNT when we assume only vdW interaction\nbetween the BN and SWCNT layers. However, we observe the elongation\nof the BNNT when a short BNNT is provided as a seed nucleus on the\nSWCNT. This grown BNNT structure, with its sharply cut edges, aligns\nwith experimental observations made using transmission electron microscopy\n(TEM). Moreover, the edge-reconstruction process favors zigzag B edges,\nwhich exhibit low edge energy according to the ReaxFF potential. Our\nsimulation successfully provides insights into the catalyst-free growth\nprocess of this one-dimensional vdW heterostructure.