Theory of B2O and BeB2 nanotubes:: New semiconductors and metals in one dimension -: art. no. 056403

We describe two new boron-based nanotubes: B2O and BeB2. Both are isoelectronic to graphite, have reasonable curvature energies, and have already been made in their bulk planar forms. The lowest energy allotrope of planar single-layer B O-2 is a semiconductor with a moderate band gap. The local density approximation band gap of the corresponding (3,0) B O-2 nanotube [similar in size to (9,0) carbon nanotube tube] is direct and around 1.6 eV, within a range inaccessible to previous C or BN nanotubes. Single-layer BeB (2) has a fascinating structure: the Be atoms rest above the boron hexagonal faces, nearly coplanar to the boron sheet. The unusual K-point pi-pi* Fermi-level degeneracy of graphite survives, while a new nearly pointlike Fermi surface appears at the M point. As a result, BeB2 nanotubes are uniformly metallic.