Line and rotational defects in boron-nitrene: Structure, energetics, and dependence on mechanical strain from first-principles calculations

A new class of point defects was recently discovered in sheets of non-stoichiometric transition metal dichalcogenides, two-dimensional (2D) materials with a trigonal prismatic lattice. Using ab initio calculations, we study the morphology and energetics of such defects, which involve 60° rotations of covalent bonds, in another 2D material with the same symmetry—hexagonal BN monolayer. We further investigate transformations of isolated vacancies into rotational defects and vacancy lines and demonstrate that agglomeration of vacancies is energetically favorable, but lines are preferable over rotational defects in the case of B-vacancies, while these defects have similar energies in N-deficient sheets. Finally, we study effects of mechanical strain on defect energetics. Our results provide microscopic insights into the thermodynamics of defects and point towards new routes to the engineering of the properties of boron-nitrene by introduction of defects and strain.