Band structure engineering of borophane by first principles calculations

Abstract

We exploited the band structure engineering in W-borophane, the most stable conformer of the fully hydrogenated borophene in the literature, by first principles calculations. Uniaxial strains along the a and b direction, biaxial strains, shear strains, H vacancy and B–H dimer vacancy defects have been considered. Our results show that uniaxial strains along the a, b directions and biaxial strain can not open the band gap for W-borophane. However, band gap opening can be achieved by applying shear strain. The shear strain induced band gap is 53 meV when the applied shear strain is only 0.01. The band gap increases with the increasing shear strain. When the shear strain reaches 0.12, the band gap can reach up to 538 meV. Two different exchange–correlation potentials have been used to confirm the band gap opening. The excellent dynamical stability of W-borophane under shear strain has been proved by the phonon dispersion, indicating that applying shear strain is an effective and feasible approach to open the band gap for W-borophane. In addition, the Dirac cone of W-borophane is maintained well under the uniaxial and biaxial strains. In free-state, the Dirac fermions of W-borophane possess an ultrahigh Fermi velocity (2.13 × 10⁶ m s⁻¹) which is higher than that of graphene. It is very interesting that the Fermi velocities of W-borophane can be tuned in a wide range of values by applying uniaxial and biaxial strain.