Point defects in hexagonal BN, BC3 and BCxN compounds studied by x-ray absorption near-edge structure

The generation of point defects in highly oriented pyrolytic boron nitride (HOPBN) after Ar+ ion bombardment in ultrahigh vacuum and subsequent exposure to air was studied by angle-resolved x-ray absorption near edge structure (XANES). The pristine HOPBN showed well-oriented boron nitride (BN) basal planes parallel to the surface, with a negligible amount of defects. Amorphization of the BN structure took place after Ar+ sputtering, as indicated by the broadening of the XANES spectra and significant decrease of the characteristic π* states. Following air exposure, the XANES analysis revealed a spontaneous reorganization of the sample structure. The appearance of four new B1s π* excitonic peaks indicates an oxygen decoration process of the nitrogen vacancies created by ion bombardment. A core-level shift model is presented to support this statement. This model is successfully extended to the case of oxygen substitutional defects in hexagonal BC3 and BCxN (0 < x < 4) materials, which can be applied to any B-based sp2-bonded honeycomb structure.