ELECTRONIC AND ATOMIC-STRUCTURE OF METASTABLE PHASES OF BORON-NITRIDE USING CORE-LEVEL PHOTOABSORPTION

Soft x-ray core-level photoabsorption has been measured from three forms of boron nitride, namely the hexagonal (hBN), cubic (cBN), and incoherent (iBN) phases. The B 1s and N 1s photoabsorption spectra of the hBN sample show evidence of both sigma*- and pi*-empty states, indicative of sp2 bonding, while the cBN absorption spectra exhibits only sp3 bonding in absorption features characteristic of the zincblende structure. The incoherent phase of BN in the form of a thin film on a Si substrate possesses sigma* and pi* states similar to hBN. The B 1s pi* absorption features of the iBN film show an angular dependence which suggests that the microstructure consists of hexagonal-phase layer planes oriented normal to the BN/Si interface.