Portugal Guilherme Ribeiro, Arantes Jeverson Teodoro
Center for Engineering, Modeling and Applied Social Science (CECS), Federal University of ABC (UFABC), Santo André, São Paulo, Brazil.
Sci Rep. 2020 May 8;10(1):7828. doi: 10.1038/s41598-020-64315-7.
Ultrathin films of perovskites have attracted considerable attention once they fit in numerous applications. Over the years, controlling and tuning their properties have been attainable when biaxial strain is applied. Through ab initio DFT calculations, (110) ultrathin (Na,K)TaO films were submitted to biaxial tensile and compressive strain. Intrinsically, surface Ta shallow states emerge into the bandgap since the (110) cleavage breaks its octahedral symmetry to create TaO units. Removal of ligands along the x-y plane stabilizes d orbitals, which decrease in energy due to lower electrostatic repulsion. Such stabilization is maximized when biaxial tensile increases the TaO planarity towards a square planar symmetry. Accordingly, the corresponding electronic levels move further into the bandgap. Conversely, compressive biaxial strain intensifies electrostatic repulsion, closing the TaO tetrahedra, and surface states move to higher energy zones. The reported strain-driven modulation might be applied in different applications, as photocatalysis, ferroelectricity, and spintronics.
钙钛矿超薄膜一旦适用于众多应用，便引起了相当大的关注。多年来，当施加双轴应变时，对其性能进行控制和调节已成为可能。通过从头算密度泛函理论（DFT）计算，（110）超薄（钠，钾）钽酸盐薄膜受到双轴拉伸和压缩应变。本质上，由于（110）解理破坏了其八面体对称性以形成TaO单元，表面Ta浅态出现在带隙中。沿x - y平面去除配体可使d轨道稳定，由于静电排斥降低，其能量降低。当双轴拉伸使TaO平面度向方形平面对称性增加时，这种稳定性最大化。相应地，相应的电子能级进一步移入带隙。相反，压缩双轴应变会增强静电排斥，使TaO四面体闭合，表面态移至更高的能量区。所报道的应变驱动调制可能应用于不同的应用，如光催化、铁电和自旋电子学。
