Stereo Boron Nitride Nanoribbons with Junction-Dependent Electronic Structures from First-Principles

Using first-principles calculations, we investigate the structures and properties of stereo triwing boron nitride nanoribbons (TBNNRs). These triwing structures are constructed by three BN ribbon wings connected via the junctions, which have comparable thermodynamic stabilities to the planar nanoribbons. We find that the junctions play a primary role in the electronic structures of triwing nanoribbons, which cause versatile electronic and magnetic properties for the stereo structures. For the armchair edges, all the TBNNRs are semiconductors, for which the wide band gaps are opened between the occupied N p(z) orbitals and unoccupied B p(z) orbitals adjacent to the junctions, while for the zigzag ones, the TBNNRs can be metals or narrow-band gap semiconductors depending on the bonding characteristics of the junctions. The sp(2)-bonding junctions substantially reduce the band gaps, and the sp(3)-bonding junctions even induce the metallic behaviors. Moreover, due to the Stoner effect, an intrinsic spin-polarized phenomenon occurs when the sp(3)-bonding junction contains only the boron atoms. Accompanied by the spin-polarization, a metal-to-semiconductor transition takes place in these zigzag TBNNRs, which become semiconducting sp-electron ferromagnets. Our studies demonstrate that the electronic structures of triwing BN nanoribbons can be effectively tailored by the junctions, which leads to potential applications in the nanoscale electronics and spintronics.