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无限层镍氧化物Nd0.8Sr0.2NiO2薄膜中超导电性的发现，建立了另一类非常规超导体，其结构和电子配对方式和铜氧化物超导体类似。不同于铜氧化物超导体的是，无限层镍氧化物仅在薄膜样品中观察到了超导性，其中界面结构、元素掺杂和无限层结构等因素是理解薄膜超导机制的关键。因此，薄膜与衬底之间的界面效应对超导机制的影响值得我们探究，然而目前对超导和非超导的镍氧化物Nd0.8Sr0.2NiOx薄膜界面结构的对比研究还没有报道过。本文基于扫描透射电镜技术，以Nd0.8Sr0.2NiO3/SrTiO3和Nd0.8Sr0.2NiO2/SrTiO3为主要研究对象，探究了镍氧化物Nd0.8Sr0.2NiOx薄膜在还原前后相分布和界面结构产生的变化，观测到界面处元素混合、原子台阶以及晶格常数变化等现象，同时发现了镍氧化物Nd0.8Sr0.2NiO2薄膜在靠近界面处1-2层单胞内未被完全还原成超导无限层结构。本研究强调了镍氧化物Nd0.8Sr0.2NiOx薄膜与衬底之间界面的原子重构及调制作用，为无限层镍基薄膜超导结构的研究提供了帮助。The discovery of superconductivity in infinite-layer nickelate Nd0.8Sr0.2NiO2 has established another type of unconventional superconductors, whose structure and electron pairing mechanism are similar to those of cuprate superconductors. Unlike cuprate superconductors, superconductivity in infinite-layer nickelates has only been observed in thin film samples, wherein heterointerface structures, elemental doping, and the infinite-layer configuration are critical for epitaxial systems. Therefore, the film-substrate interfacial effects require exploration for understanding superconductivity. However, comparative studies on the interfacial structures between superconducting and nonsuperconducting Nd0.8Sr0.2NiOx nickelate thin films have not been reported in the literature.
This work focuses on Nd0.8Sr0.2NiO3/SrTiO3 and Nd0.8Sr0.2NiO2/SrTiO3 and utilizes scanning transmission electron microscopy (STEM) to conduct a detailed characterization of the phase distribution and interfacial structural variation in the superconducting and non-superconducting nickelate thin films. Further analysis of the corresponding atomic HAADF、 iDPC images and EDS maps reveals the phenomena such as elements mixing, atomic steps, and changes in lattice parameters at the interfaces. These results also show that in the Nd0.8Sr0.2NiO2 film, the first 1-2 unit cells near the interface have not been fully reduced to the superconducting infinite-layer structure. Such findings contribute to alleviating the strong polarity discontinuity at the sharp interface.
This study emphasizes the atomic reconstruction and the modulation effect at the interface between the substrate and the film, enriching the understanding of the structural properties of the Nd0.8Sr0.2NiOx films, and providing crucial experimental evidence for understanding the interfacial structure of infinite-layer nickelates. -
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