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 <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:msub><a:mi>LaAlO</a:mi><a:mn>3</a:mn></a:msub></a:math> (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 <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mn>5</b:mn><b:mi>d</b:mi></b:math> states may act as a charge reservoir stabilizing the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:mn>4</c:mn><c:msup><c:mi>f</c:mi><c:mn>5</c:mn></c:msup></c:mrow></c:math> configuration in the nitrogen-deficient compound. The spectra also reveal a significant hybridization of the Sm <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mn>4</d:mn><d:mi>f</d:mi></d:math> and N <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:mn>2</e:mn><e:mi>p</e:mi></e:math> states.