B and N K-edge spectra have been acquired on both single-phase BN powders and on BN/Si films fabricated using ion-assisted pulsed-laser deposition. Comparison with the powder data shows the films to be primarily sp2-bonded. Systematic differences between the films' spectra and that of pure hBN suggest that another phase is present, probably the cBN that has been observed with infrared transmission measurements. Three sharp peaks appear in the films' B K-edge spectra between the usual pi* and sigma* bands. These peaks may be related to disorder or may indicate the presence of the rBN phase in the films. Angle-dependent x-ray absorption studies have shown that the BN/Si films are preferentially oriented with the hexagonal axis nearly in the film plane. Transmission electron microscopy and photoemission studies are underway to help clarify issues of film morphology and stoichiometry. The near-edge x-ray absorption spectra of thin BN films are proving to be more complex to interpret than those of vapor-deposited C films.
We would like to thank A.K. Ballal and L. Salamanca Riba for the TEM pictures, D.K. Shuh for assistance with the data collection and E.A. Hudson for helpful discussions. Part of this work was performed under the auspices of the U.S. Department of Energy by LLNL under contract No. W-7405-ENG-48.