increasing from 6 K at 160 GPa to 11 K at 250 GPa. This structural transformation occurs at pressures at which theory predicts the icosahedra will dissociate. Speculation as to the structure of this phase has included face-centred cubic (analogous to Al); α-Ga, and body-centred tetragonal (analogous to In). It has also been suggested that the nonmetal-metal transition is simply the result of a band gap closure, as occurs with iodine, rather than a structural transition. Borophene There exist several two-dimensional forms of boron (together called borophenes), and even more are predicted theoretically. Borospherene The discovery of the quasispherical allotropic molecule borospherene (B40) was announced in July 2014. Amorphous boron Amorphous boron contains B12 regular icosahedra that are randomly bonded to each other without long range order. Pure amorphous boron can be produced by thermal decomposition of diborane at temperatures below 1000 °C. Annealing at 1000 °C converts amorphous boron to β-rhombohedral boron. Amorphous boron nanowires (30–60 nm thick) or fibers can be produced by magnetron sputtering and laser-assisted chemical vapor deposition, respectively; and they also convert to β-rhombohedral boron nanowires upon annealing at 1000 °C. Notes References Bibliography External links Boron