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Surface and interface effects in oxygen-deficient SrMnO3 thin films grown on SrTiO3
Moloud Kaviani1, Ulrich Aschauer1
1Department of Chemistry, Biochemistry and Pharmaceutical Sciences, University of Bern, Freiestrasse 3, CH-3012 Bern, Switzerland. ulrich.aschauer@unibe.ch.
Physical Chemistry Chemical Physics : PCCP
|January 31, 2022
Summary
Oxygen vacancies in strontium manganite (SrMnO3) thin films prefer surface regions due to undercoordination. This defect behavior differs significantly from bulk materials, impacting complex oxide functionality.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Surface Science
Background:
- Complex oxide functionality (ferroelectricity, magnetism, superconductivity) is often realized in epitaxial thin films.
- Oxygen vacancies are dominant defects in oxides, but their behavior in thin films is poorly understood compared to bulk.
- Thin-film geometries introduce interfaces and surfaces, altering defect stability and electronic structure.
Purpose of the Study:
- To investigate the stability and electronic structure of oxygen vacancies in SrMnO3 (SMO) thin films on SrTiO3 (STO) substrates.
- To compare defect behavior in thin films with that of bulk or strained bulk materials.
- To understand the influence of surface and interface effects on oxygen vacancy formation and properties.
Main Methods:
- Density functional theory (DFT) calculations were employed.
- The model system studied was a SrMnO3 thin film epitaxially grown on a SrTiO3 (001) substrate.
- Analysis focused on structural and electronic differences arising from the thin-film geometry.
Main Results:
- Undercoordination at the film surface leads to structural and electronic differences compared to bulk SMO.
- A changed crystal field causes valence-band state depletion and charge transfer to surface Mn atoms.
- Oxygen vacancies show a strong preference for the surface region over deeper layers in the thin film.
- Metastable oxygen vacancies in the substrate exhibit spatial separation of the defect from its excess charge, which localizes in the film near the substrate boundary.
Conclusions:
- Surface and interface effects significantly alter the stability and electronic structure of oxygen vacancies in thin films.
- The findings highlight the distinct defect chemistry in thin-film complex oxides compared to bulk.
- Understanding these surface/interface effects is crucial for designing and optimizing functional oxide thin films.
