Electron spectroscopy on boron nitride thin films: Comparison of near-surface to bulk electronic properties

Combining spectroscopic methods probing both occupied as well as unoccupied electronic states, the surface electronic structure of ex situ prepared boron-nitride films is analyzed and compared to experimental and theoretical bulk-electronic properties taken from the literature. X-ray photoelectron spectroscopy is applied to probe the core-level and valence-band electronic states, electron-energy-loss spectroscopy in the reflection geometry to investigate conduction band states as well as excitations like plasmons and core excitons. For films with hexagonal structure, the results from the near-surface region are found to reflect both the ground state and the many-body properties of the bulk material. Cubic boron nitride films in all cases exhibit a hexagonal-like top layer with a thickness of about 0.9 nm. Low-energy ion bombardment at room temperature is found to significantly increase the amount of disorder in both types of films, leading to the transformation of the cubic phase into a hexagonal-like material.