A Causal Relationship Between Boron Seeds and the Selectivity and Growth Mode of Boron Nitride Nanotubes in Inductively‐Coupled Plasma

We investigate a relationship between the size and abundance of boron (B) seeds and the selectivity of BNNTs in an inductively-coupled plasma. Key parameters influencing the size and abundance of B seeds are discussed in relation to their impact on the selectivity of BNNTs versus other BN structures. Our statistical analysis suggests that the amount of BNNTs in the as-produced material scales with B seed abundance. B partial pressure, adjusted through feedstock's feed rate, controls the seeds' abundance while maintaining their size range. The turbulence intensity and residence time in the B droplet formation zone, adjusted through the plasma power, influence both the size and abundance of seeds. Higher turbulence and longer residence times generally lead to larger seeds and broader size distributions. These two variables affect the cooling rate in the B seed-BNNT formation zone, which inversely correlates with the seed size. Notably, BNNT diameters are consistent across all the tested conditions despite the seed size differences. We attribute this consistency to the growth mode, which is a hybrid of tangential and perpendicular modes, giving the seed-tube structure a golf club-like appearance. The perpendicular component is speculated to minimize the dependence of the nanotube diameter on the seed diameter.