PbTiO3/SrTiO3超晶格中埋藏极性拓扑结构的深度分辨演化
Depth-Resolved Evolution of Buried Polar Topologies in a PbTiO3/SrTiO3 Superlattice
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中文总结 AI 辅助
本研究结合多种先进电子显微技术，直接可视化PbTiO3/SrTiO3超晶格中埋藏极性拓扑的深度演化，揭示了表面与内部极性结构的差异，为研究复杂氧化物纳米结构的埋藏功能态提供了新方法。
中文摘要 AI 辅助
复杂氧化物中的极性拓扑结构可产生丰富的新奇功能，且从根本上受三维（3D）原子结构调控。然而，埋藏的三维极性构型的直接实验测定仍是长期存在的挑战，因为传统的（扫描）透射电子显微镜（(S)TEM）主要提供投影结构信息，深度敏感性有限。本文中，我们结合深度切片低角环形暗场（LAADF）STEM、高角ADF（HAADF）STEM以及多层电子ptychography（MEP），直接可视化PTO/STO超晶格中与深度相关的原子结构和极性拓扑结构。深度切片STEM显示出明显的焦深依赖对比度变化以及Pb原子列的表观分裂，表明沿电子束方向存在显著的结构异质性。MEP重构同时以纳米级深度分辨率分辨了Pb、Ti和O亚晶格，实现了重构体积内原子位移的定量映射。所得三维原子模型揭示了Pb、Ti和O原子的显著深度依赖位移，以及极性拓扑结构的相应演化。在样品表面附近观察到涡旋状极性结构，但在内部区域被强烈抑制，内部区域出现了不同的极性构型。这些发现表明，传统投影图像中观察到的极性图案可能源于多种深度依赖极性状态的叠加，可能掩盖了潜在的三维极性纹理。我们的发现建立了局部原子位移与深度依赖极性拓扑结构之间的直接实验联系，为研究和设计复杂氧化物纳米结构中的埋藏功能态开辟了新机遇。
英文摘要
Polar topologies in complex oxides gives rise to a rich spectrum of emergent functionalities and are fundamentally governed by three-dimensional (3D) atomic structures. However, direct experimental determination of buried 3D polar configurations remains a longstanding challenge because conventional (scanning) transmission electron microscopy ((S)TEM) provides primarily projected structural information with limited depth sensitivity. Here, we combine depth-sectioning low-angle annular dark-field (LAADF) STEM, high-angle ADF (HAADF) STEM, and multislice electron ptychography (MEP) to directly visualize the depth-dependent atomic structure and polarization topology in a PTO/STO superlattice. Depth-sectioning STEM reveals pronounced focal-depth-dependent contrast variations and apparent splitting of Pb atomic columns, indicating significant structural heterogeneity along the beam direction. MEP reconstruction simultaneously resolves the Pb, Ti, and O sublattices with nanometer-scale depth resolution, enabling quantitative mapping of atomic displacements throughout the reconstructed volume. The resulting 3D atomic model reveals substantial depth-dependent displacements of Pb, Ti, and O atoms and a corresponding evolution of the polarization topology. Vortex-like polarization structures are observed near the specimen surfaces but become strongly suppressed within the interior, where distinct polarization configurations emerge. These findings show that polarization patterns observed in conventional projection images can arise from the superposition of multiple depth-dependent polar states and may obscure the underlying 3D polarization texture. Our findings establish a direct experimental link between local atomic displacements and depth-dependent polarization topology, opening new opportunities for investigating and engineering buried functional states in complex oxide nanostructures.
