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O: Fachverband Oberflächenphysik

O 66: Poster Session V: 2D Materials: Electronic structure, excitations, etc. I

O 66.7: Poster

Wednesday, March 3, 2021, 10:30–12:30, P

Surface and interface effects in oxygen deficient SrMnO₃ thin films grown on SrTiO₃ — •Moloud Kaviani and Ulrich Aschauer — Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, CH-3012 Bern, Switzerland

Complex oxide functionality, such as ferroelectricity, magnetism or superconductivity, is often achieved in epitaxial thin-film geometries. Oxygen vacancies tend to be the dominant type of defect in these materials but a fundamental understanding of their stability and electronic structure has so far only been established in the bulk or strained bulk, neglecting interfaces and surfaces present in the thin-film geometry. We investigate here by first-principles calculations, oxygen vacancies in the model system of a SrMnO₃ (SMO) thin-film atop a SrTiO₃ (STO) (001) substrate. We establish structural and electronic differences compared to bulk SMO that, in addition to misfit strain result also from under-coordination at the film surface. We then study the stability and electronic structure of oxygen vacancies in both the thin-film and the substrate, showing that electrostatics render oxygen vacancies more stable towards the film surface. As opposed to bulk SMO, we observe only partial reduction of Mn⁴⁺ to Mn³⁺ and for oxygen vacancies in SrO layers, a reduction of Mn only in the layer below the vacancy. We relate this to crystal field changes at the surface, that strongly alter the defect chemistry in the film. Our results show that surface and interface effects lead to significant differences in stability and electronic structure of oxygen vacancies in thin-film geometries compared to the (strained) bulk.