A comprehensive study of different local bonding environments in boron nitride-bulk and thin filmshas been performed by core level photoabsorption. Several new features not present in crystalline reference samples are found in the absorption spectra of the thin films. These are identified as nitrogen vacancies in the hexagonal bonding of BN, nitrogen interstitials, boron clustering, sp 3-like metastable phases and sp 3 phases. Quantitative information on the concentration and distribution of point defects is easily extracted from the photoabsorption data and is discussed with regard to formation of riew phases, the B :N ratio in the films, and compared with a random model of defect formation. Information on the stability of the new bonding environments is gained by annealing the thin films. Modification of the orientation of the sp 2 hexagonal planes is attained by ion bombardment and annealing, and is monitored by angle resolved photoabsorption.
Near-edge x-ray absorption fine structure (NEXAFS) has been used to study the defect content and the bonding modifications induced in BN thin films by ion implantation. The initial films were hexagonal-like BN grown on Si(100) by pulsed laser deposition. Subsequent ion implantation with N2+ at 180 keV induces the formation of a significant proportion of sp3 bonding (cubic-like), and the formation of nitrogen void defects in the remaining sp2 BN. These modifications in the bonding of a film lacking long range order can only be distinguished with a local order technique like NEXAFS.
High resolution and symmetry resolved corelevel spectroscopy using soft xray undulator (invited) Rev. Sci.Core-level photoabsorption has been used to determine the sp 2 and sp 3 bonding content of nanocrystalline diamond thin films grown using C 60 or CH 4 precursors. The C͑1s͒ absorption spectra show clear bulk diamond excitonic and sp 3 features with little evidence of sp 2 bonding, while the Raman spectra measured from these same films are ambiguous and indeterminate. This result can be attributed to the local structure ͑near-neighbor bonding͒ sensitivity of core-level photoabsorption that is insensitive to domain size, unlike Raman spectroscopy.
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