Title:New Catalyst for the Growth of Clean and Small-Diameter Boron Nitride Nanotubes

Boron Nitride Nanotubes (BNNTs), are structurally similar to carbon nanomaterials (CNTs), constructed by sp2 hybridized atoms that are arranged in a hexagonal network. The electrically insulating and optically transparent nature of BNNTs makes them unique for advanced electronics [1-2] and biomedical applications [3-4]. The synthesis of clean BNNTs is important for these applications, which we reported, based on the catalytic chemical vapor deposition (CCVD) using MgO, Ni, and Fe catalysts [5-7]. The diameters of these clean and high-quality BNNTs range between 20-60nm. Nevertheless, achieving and controlling small diameters (below 20 nm) remains a challenge.

Here we gain insights into the catalytic performance that is essential for achieving improved diameter control of high-quality and high-purity BNNTs. Employing the growth-vapor trapping (GVT) approach [5, 6] within a conventional tube furnace, we have revealed the function of a series of magnesium-based catalysts for the growth of small-diameter BNNTs. Specifically, we found a catalyst that we could control its concentration, therefore the particle size of the catalyst during growth. We found that when the catalyst concentrations are lower, there are fewer nucleation sites for BNNT formation, but the diameters are small ~10-15nm. At intermediate concentrations, we could grow dense and pure BNNTs with slightly larger diameters. We further revealed several key parameters of GVT that allow us to control the diameter and growth density of BNNTs. Details of the synthesis approach, the new catalysts, and results based on scanning electron microscopy (SEM) and transmission electron microscopy (TEM) will be discussed at the conference.