Oxygen-stabilized triangular defects in hexagonal boron nitride

Recently several experimental transmission electron microscopy (TEM) studies have reported the observation of nanoscale triangular defects in mono- and multilayer hexagonal boron nitride (h-BN). First-principles calculations are employed to study the thermodynamical stability and spectroscopic properties of these triangular defects and the chemical nature of their edge termination. Oxygen-terminated defects are found to be significantly more stable than defects with nitrogen-terminated edges. Simulated x-ray absorption spectra of the boron K edge for oxygen-terminated defects show excellent agreement with experimental x-ray absorption near-edge spectroscopy (XANES) measurements on defective h-BN films with oxygen impurities. Finally, we show that the structural model for oxygen defects in h-BN as deduced from the simulated core-level spectroscopy is intrinsically linked to the equilateral triangle shape of defects as observed in many recent electron microscopy measurements.