Half-metallicity modulation of hybrid BN-C nanotubes by external electric fields: A first-principles study

On the basis of density functional theory, we systematically investigate the electronic and magnetic properties of hybrid BN-C nanotubes, C _x(BN)_y where x + y = 12, with and without an external electric field. The BN-C nanotubes are totally distinct from pristine boron-nitride and carbon nanotubes. The electronic properties of C _x(BN)_y change significantly with composition: from the nonmagnetic semiconductors to the half-metals. The half-metallicity is attributed to the competition among the band gap, which is related to the width of C domain, the width of BN domain, and the intrinsic polarization field. Application of the external fields can enhance or counterbalance the polarization fields and change the band gaps. The half-metallicity can be modulated. In BN-rich tubes, such as C₂(BN)₁₀, the energy gap can be engineered from 0.50 eV to 0.95 eV and in C₃(BN) ₉, the ground state is converted from the nonmagnetic state into the anti-ferro-magnetic one. In other tubes, the half-metallicity can be enhanced or destroyed by different external fields. The modulation indicates that hybrid BN-C nanotubes can work as the components of the spin-filter devices.