Boron nitride nanotubes (BNNTs) have attracted great attention because of their extraordinary thermal, mechanical, electronic, and optical properties. However, the applications of BNNTs have been hampered by the limited yield of the synthesized materials. To gain insight into the growth process we have studied key mechanisms for root growth of BNNTs on the surface of a liquid boron droplet by ab initio molecular dynamics simulations. We find that nitrogen atoms reside predominantly on the droplet surface where they organize to form boron nitride islands below 2400 K. To minimize contact with the liquid particle underneath, the islands assume non-planar configurations that are likely precursors for the thermal nucleation of cap structures. Once formed, the caps are stable and can easily incorporate nitrogen and boron atoms at their base, resulting in further growth. Our simulations support the root-growth mechanism of BNNTs and provide comprehensive evidence of the active role played by liquid boron.

Reference:

• "Root-Growth of Boron Nitride Nanotubes: Experiments and ​Ab Initio Simulations", B. Santra, H.-Y. Ko, Y.-W Yeh, F. Martelli, I. Kaganovich, Y. Raitses, and R. Car. Nanoscale, DOI: 10.1039/C8NR06217J (2018) [arxiv]