Electronic structure of boron nitride single crystals and films

Abstract

We present a comparison between experimental soft x-ray spectra and density of states calculations of hexagonal boron nitride ($h$-BN) and cubic boron nitride ($c$-BN) single crystals. Cubic boron nitride films, grown on both mirror and scratched single crystal silicon wafers, have also been investigated using soft x-ray absorption spectroscopy (XAS) and soft x-ray emission spectroscopy (XES). Spectra measured at the $1s$ thresholds of boron and nitrogen give a complete picture of the occupied and unoccupied partial density of states for these materials. The films are shown to be a mixture of $s{p}^{3}$ bonded nanocrystalline $c$-BN phase and $s{p}^{2}$ bonded $h$-BN phase. As the roughness of the deposition surface increases, a decrease in the amount of $s{p}^{3}$ phase in the resulting film is observed. There are clear differences between the electronic structures of the nanocrystalline films and the single crystal samples. No differences between the spectra of the single crystals and previously reported measurements on powder samples of BN were observed.