Electronic properties and stability phase diagrams for cubic BN surfaces

This contribution investigates structural and electronic properties as well as stability phase diagrams of surfaces of the cubic boron nitride (c-BN). Our calculated parameters for bulk c-BN agree reasonably well with both experimental and computed values available in the literature. Based on the energies of the three experimentally recognised phases of bulk boron, i.e. α-B₃₆, β-B₁₀₅ and γ-B₂₈, we estimate enthalpy of formation of c-BN to be −2.8 eV. The c-BN(1 0 0) surface offers separate B and N terminations (denoted as c-BN(1 0 0)_B and c-BN(1 0 0)_N), whereas c-BN(1 1 1) and c-BN(1 1 0) are truncated with combinations of boron and nitrogen atoms (denoted as c-BN(1 1 1)_BN and c-BN(1 1 0)_BN). Optimised geometries of surfaces display interlayer displacements up to the three topmost layers. Downward displacement of surface boron atoms signifies a common geometric feature of all surfaces. Bulk c-BN and its most stable surface c-BN(1 0 0)_N possess no metallic character, with band gaps of 5.46 and 2.7 eV, respectively. We find that, only c-BN(1 0 0)_B configuration exhibits a metallic character. c-BN(1 1 0)_BN and c-BN(1 1 1)_BN surfaces display corresponding band gaps of 2.5 and 3.9 eV and, hence, afford no metallic property.