Despite recent successes in the synthesis of boron nanotubes (BNTs) many questions about their atomic structure and other basic properties do remain.
We found by means of first-principles molecular dynamics simulations that free-standing, single-wall BNTs with diameters larger than 0.6 nm are thermally stable at the experimentally reported synthesis temperature of 870C and higher. The walls of thermally stable BNTs have a variety of different mixed triangular-hexagonal morphologies [1]. Our results indicate that mixed triangular-hexagonal morphologies are structural paradigm for atomically thin boron.
We further studied the impact of structural disorder on the charge transport properties of BNTs. In the limit of low defect concentrations the metallic BNTs strongly screen individual defects. As result the defect-induced reduction of the electrical conductance as compared to ideal BNTs depends merely on the number of defects but is almost independent of their type, relative position and the geometry of the BNT. These results show that BNTs are highly conductive even in presence of structural defects.
Furthermore, we show how chemical functionalization of single-walled BNTs can tune the basic electronic properties from metallic to semiconducting. The effect can be achieved by atoms or functional groups which have different chemical bonding interactions with BNTs. Our results indicate that functionalization of BNTs offers chirality independent control of the electronic structure of the nanotubes, which is paramount for industrial applications.