Influence of nitrogen stoichiometry and the role of Sm 5d states in SmN thin films

We report a comprehensive study of the synthesis of epitaxial SmN thin films on ${\mathrm{LaAlO}}_3$ (100) by molecular beam epitaxy under slow-growth conditions. By carefully tuning the substrate temperature and the molecular nitrogen partial pressure, we are able to control the nitrogen content of our samples and produce near-stoichiometric, well-ordered SmN thin films. The influence of nitrogen defects on the samarium ion valence and the electronic structure is investigated by x-ray absorption and photoelectron spectroscopy, suggesting that the empty Sm $5d$ states may act as a charge reservoir stabilizing the $4f^5$ configuration in the nitrogen-deficient compound. The spectra also reveal a significant hybridization of the Sm $4f$ and N $2p$ states.