Boron nitride nanotubes (BNNTs)

Boron nitride nanotubes (BNNTs) are isoelectronic and isostructural with carbon nanotubes (CNTs), which are cylinders with diameters on the order of nanometers and lengths usually on the order of micrometers, but which may extend to millimeters or more. The carbon atoms in CNTs are substituted by alternating boron and nitrogen atoms in BNNTs. BNNTs were first synthesized by Alex Zettl in 19951 following theoretical predictions by Marvin Cohen2. They are one of the few advanced materials whose existence was predicted before discovery. However, the properties of BN nanotubes are very different from carbon nanotubes: whereas CNTs can be metallic or semiconducting depending on the rolling direction and radius, a BNNT is an electrical insulator with a bandgap between 5.5 and 5.9 eV. Unlike for CNTs, this bandgap can be tuned either by applying a bias voltage or by substituting carbon atoms in the BNNT structure, so that the lower bandgap limit can be extended to about 0.2 eV. The arrangement of alternating boron and nitrogen atoms gives BNNTs a corrugated surface and some degree of ionic bonding, so they attach more readily to other molecules and to themselves.