Theory of and Nanotubes: New Semiconductors and Metals in One Dimension

We describe two new boron-based nanotubes: and. 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 is a semiconductor with a moderate band gap. The local density approximation band gap of the corresponding nanotube [similar in size to carbon nanotube tube] is direct and around 1.6 eV, within a range inaccessible to previous or nanotubes. Single-layer has a fascinating structure: the atoms rest above the boron hexagonal faces, nearly coplanar to the boron sheet. The unusual Fermi-level degeneracy of graphite survives, while a new nearly pointlike Fermi surface appears at the point. As a result, nanotubes are uniformly metallic.