Evolution of Irradiation-Induced Vacancy Defects in Boron Nitride Nanotubes.

Irradiation-induced vacancy defects in multiwalled (MW) boron nitride nanotubes (BNNTs) are investigated via in situ high-resolution transmission electron microscope operated at 80 kV, with a homogeneous distribution of electron beam intensity. During the irradiation triangle-shaped vacancy defects are gradually generated in MW BNNTs under a mediate electron current density (30 A cm(-2)), by knocking the B atoms out. The vacancy defects grow along a well-defined direction within a wall at the early stage as a result of the curvature induced lattice strain, and then develop wall by wall. The orientation or the growth direction of the vacancy defects can be used to identify the chirality of an individual wall. With increasing electron current density, the shape of the irradiation-induced vacancy defects changes from regular triangle to irregular polygon.