Abstract
HRTEM study has been carried out on BN nanotubes produced by laser heating of hBN in a diamond anvil cell under high nitrogen pressure of 8.3 GPa Special attention has been paid to their tip-end capping features and the epitaxial relationship with the mother phase during their growth. The observed tip-end cone angles ranged from 22 degrees to 45 degrees. The tip-end structural models have been proposed that are relied on the existence of 4 and 8 member BN rings in die nanotube caps instead of 5 and 7 member rings which are typical for carbon nanotubes. The base material in the bottom of the nanotubes mostly revealed cubic BN structure, though occasionally, hexagonal BN was found as the nanotube mother phase. In the former case, cBN in the bottom of the nanotube and the nanotube hBN sheets exhibit orientation relationship as follows: (110)(cubic)//(0002)(hex) and [<(1)over bar 11>](cubic)//[<10(1)over bar 0>](hex).