Structure of boron nitride nanotubules

We have used high-resolution transmission electron microscopy to resolve the [0001] projected basal plane structure and chirality relationships in boron nitride nanotubes. Evidence for tube growth along both < 10 (1) over bar0 > and < 11 (2) over bar0 > is found. Our results suggest that the < 11 (2) over bar0 > (armchair) tubes form first. Subsequent growth can take the form of a < 10 (1) over bar0 > (zig-zag) tube or additional armchair tubes. In both cases, the additional walls can be accommodated without the need for defect formation for circumferential tube closure. These results suggest that real boron nitride tubes may, in practice, realize their inherently high modulus and display less variation of mechanical properties than tubes comprised of carbon. (C) 2001 American Institute of Physics.