在 SrTiO3 上生长的缺氧 SrMnO3 薄膜的表面和界面效应,Physical Chemistry Chemical Physics

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在 SrTiO3 上生长的缺氧 SrMnO3 薄膜的表面和界面效应
Physical Chemistry Chemical Physics ( IF 2.9 ) Pub Date : 2022-01-31 , DOI: 10.1039/d1cp04998d
Moloud Kaviani ₁ , Ulrich Aschauer ₁

Affiliation

复杂的氧化物功能，例如铁电性、磁性或超导性通常在外延薄膜几何结构中实现。氧空位往往是这些材料中的主要缺陷类型，但迄今为止，对其稳定性和电子结构的基本了解大多建立在体或应变体中，忽略了薄膜几何形状中存在的界面和表面。我们在这里通过密度泛函理论计算研究了在 SrTiO _{3上生长的 SrMnO}₃ (SMO) 薄膜模型系统中的氧空位(STO) (001) 基板。与散装 SMO 相比，结构和电子方面的差异主要是由于薄膜表面的配位不足。改变的晶体场导致次表面价带状态的耗尽和该电荷转移到表面Mn原子，这两者都强烈影响薄膜中的缺陷化学。结果是与更深层相比，表面区域中的氧空位强烈偏好。最后，对于衬底中的亚稳态氧空位，我们预测缺陷与其过量电荷的空间分离，后者被容纳在薄膜中但靠近衬底边界。这些结果表明，与（应变）体相比，表面和界面效应导致薄膜几何形状中氧空位的稳定性和电子结构存在显着差异。

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Surface and interface effects in oxygen-deficient SrMnO3 thin films grown on SrTiO3

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 mostly been established in the bulk or strained bulk, neglecting interfaces and surfaces present in a thin-film geometry. We investigate here, via density functional theory calculations, oxygen vacancies in the model system of a SrMnO₃ (SMO) thin film grown on a SrTiO₃ (STO) (001) substrate. Structural and electronic differences compared to bulk SMO result mainly from undercoordination at the film surface. The changed crystal field leads to a depletion of subsurface valence-band states and transfer of this charge to surface Mn atoms, both of which strongly affect the defect chemistry in the film. The result is a strong preference of oxygen vacancies in the surface region compared to deeper layers. Finally, for metastable oxygen vacancies in the substrate, we predict a spatial separation of the defect from its excess charge, the latter being accommodated in the film but close to the substrate boundary. These 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.

更新日期：2022-01-31

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