Direct observation of defect levels in hexagonal BN by soft X-ray absorption spectroscopy

Formation of defects in hexagonal boron nitride under low-energy argon bombardment has been studied by near-edge X-ray absorption fine structure (NEXAFS) around B and N K-edges. Breaking of B–N bonds and creation of nitrogen vacancies has been identified from the B K-edge, followed by the formation of molecular nitrogen, N2, at interstitial positions. The presence of N2 produces a sharp resonance in the low-resolution NEXAFS spectra around N K-edge, showing the characteristic vibrational fine structure in high-resolution measurements. Several new peaks in NEXAFS spectra have been assigned to boron or nitrogen interstitials, in good agreement with theoretical predictions.