High-purity straight and discrete multiwalled boron nitride nanotubes (BNNTs) were grown via a boron oxide vapor reaction with ammonia using LiNO₃ as a promoter. Only a trace amount of boron oxide was detected as an impurity in the BNNTs by energy-dispersive X-ray (EDX) and Raman spectroscopies. Boron oxide vapor was generated from a mixture of B, FeO, and MgO powders heated to 1, 150 ℃, and it was transported to the reaction zone by flowing ammonia. Lithium nitrate was applied to the upper side of a BN bar from a water solution. The bar was placed along a temperature gradient zone in a horizontal tubular furnace. BNNTs with average diameters of 30-50 nm were mostly observed in a temperature range of 1, 280-1, 320 ℃. At higher temperatures, curled polycrystalline BN fibers appeared. Above 1, 320 ℃, the number of BNNTs drastically decreased, whereas the quantity and diameter of the fibers increased. The mechanism of BNNT and fiber growth is proposed and discussed.

We have investigated the behavior of two nanotube systems, carbon and boron nitride, under controlled applied voltages in a high-resolution transmission electron microscope (TEM) equipped with a scanning tunneling microscope (STM) unit. Individual nanotubes (or thin bundles) were positioned between a piezo-movable gold electrode and a biased (up to ±140 V) STM tip inside the pole-piece of the microscope. The structures studied include double- and multi-walled carbon nanotubes (the latter having diverse morphologies due to the various synthetic procedures utilized), few-layered boron nitride nanotube bundles and multi-walled boron nitride nanotubes (with or without functionalized surfaces). The electrical breakdown, physical failure, and electrostatic interactions are documented for each system.