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近年来，无限层镍氧化物薄膜作为首个实现超导电性的镍氧化物体系，引起研究者广泛关注.该材料通过将钙钛矿结构前驱体去除顶角氧获得.传统的CaH2封管还原法虽简单有效，但属于非原位手段且容易造成表面非晶化，不适用于表面敏感实验的研究.为了解决该问题，本文在超高真空腔体中建立了三种不同的原位原子氢还原方式(科研用射频等离子体裂解源、工业用射频等离子体裂解源和热裂解源)，系统探索各自的最优还原条件，并比较不同还原方式对薄膜表面形貌和超导转变温度等性质的影响.多种原位还原方式的优化和对比对于进一步提升无限层镍氧化物的表面质量及超导性能至关重要.结果表明，三种原位手段在降低薄膜表面粗糙度方面相比于CaH2还原表现出优势，工业用射频等离子体裂解源和热裂解源可实现优于CaH2的超导性能.研究还系统介绍了各还原方式的参数优化结果，为实现高质量无限层镍氧化物薄膜的可控还原提供了重要参考.Infinite-layer nickelates, obtained by removing the apical oxygen from perovskite precursors, are the first nickelate system to exhibit superconductivity and provide a platform for exploring unconventional superconductivity. Although the traditional CaH2 sealed-tube reduction method is simple and effective, it is an ex-situ process that tends to cause surface contamination or degradation, making it unsuitable for surfacesensitive measurements like ARPES. To address this issue, we established three different in-situ atomic hydrogen reduction methods in an ultrahigh vacuum chamber-namely, a lab-based RF plasma cracker, an industrial RF plasma cracker, and a thermal gas cracker. Comprehensive optimization of key parameters-including hydrogen flow, RF power or filament temperature, reduction temperature, and time-was carried out for each method. Structural evolution was monitored by X-ray diffraction (XRD), surface morphology was characterized by atomic force microscopy (AFM), and superconducting properties were examined through electrical transport measurements. The results demonstrate that all three in-situ methods can achieve reduction and superconducting properties comparable to or better than CaH2 reduction. Moreover, all atomic hydrogen approaches yield lower surface roughness than CaH2 from the same precursor, highlighting their clear advantage in enhancing surface flatness. Notably, the industrial RF plasma source, owing to its higher hydrogen production efficiency, enables sufficient reduction under milder conditions, resulting in even smoother surfaces. This study also provides a detailed summary of the parameter optimization for each method, offering valuable guidance for the controlled reduction of high-quality infinite-layer nickelate thin films.
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Keywords:
- Infinite-layer nickelate /
- unconventional superconductor /
- in-situ atomic hydrogen reduction
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