铁电薄膜界面精细结构以及性能调控的研究

Perovskite oxide materials have a wide range of applications due to their excellent properties. In 2001, Nobel Laureate in Physics H. Kroemer mentioned in his award speech that the interface is the device. Although this interface refers to semiconductor materials, it has become a hot spot in oxide research. Interfaces will become especially important when ferroelectric materials need to be applied to miniaturized equipment. The interface is divided into a homogenous interface and a heterogeneous interface. The two interfaces have similarities and can interact with each other. Therefore, this project firstly plans to construct a heterogeneous interface to control the phase transition of ultra-thin PbTiO3 film. Combined with experimental conditions such as aberration-corrected electron microscopy and piezoelectric microscopy, the fine structure and property modulation of the film are revealed. It is intended to extract the strain state in an ultrathin film by measuring the position coordinates of different ion. Combined with the experimental means, the law of performance changes caused by the structure is given. Secondly, it is proposed to study the evolution of the structure with the thickness of the film by designing the complex domain configuration formed by the interaction between the domain wall in the homogenous interface and the heterogeneous interface. The completion of the project not only can systematically understand the variation of more atomic structure of PbTiO3 film, but also provide important atomic structure information for profound understanding of the variation law of domain configuration.

钙钛矿氧化物材料由于具有优异的性能，应用范围十分广泛。2001年，诺贝尔物理学奖获得者H.Kroemer在获奖感言中就提到界面就是器件。该界面虽然是指半导体材料，但是在氧化物研究中开始成为一大热点。当铁电材料需以超薄的尺度应用在小型化设备上时，界面将变得尤其重要。界面分为同质界面和异质界面，两种界面具有相似性，又可以相互作用。本项目首先拟建筑异质界面来调控出超薄PbTiO3薄膜的相变，结合像差校正透射电子显微技术与压电力显微镜等实验方法，揭示该薄膜精细结构以及对性能的调控。拟通过测量不同离子的坐标位置，提取超薄薄膜中应变状态。结合实验手段，给出结构引起性能的变化等规律。其次拟设计出同质界面中的畴壁与异质界面相互作用形成的复杂畴组态，研究其结构随着薄膜厚度的演变规律。项目的完成不仅可以系统性认识PbTiO3薄膜的原子结构的变化规律，而且为深刻理解畴组态的变化规律提供重要的原子结构信息。

大量的研究证明钙钛矿氧化物铁电薄膜具有优异的铁电性能，能够在铁电存储器等电子设备上得到广泛应用。但是，由于受到畴结构调控不均以及界面退极化场造成地严重地影响等问题，需要进一步地深入研究。基于此，本项目以PbTiO3薄膜为研究对象，首先构建了PbTiO3/SrTiO3多层膜体系，在无应力SrTiO3衬底上得到了三种不同地复杂闭合畴结构，分析了三种复杂畴结构地晶格常数以及铁电极化等微观信息，得出了通过调控底层 PbTiO3薄膜厚度并改变 PbTiO3薄膜厚度比以获得不同的通量闭合畴。其次构建了不同地电极与PbTiO3薄膜地异质界面，发现在SrRuO3电极上生长的超薄PbTiO3薄膜，在PbTiO3薄膜内部靠近电极界面处一个单胞出现了面外晶格常数以及离子位移锐减的现象，而在Nb:SrTiO3上生长的薄膜未发现该现象，而在La0.7Sr0.3MnO3电极上生长的PbTiO3薄膜内部靠近电极界面处一个单胞出现了相反现象，也就是相应的物理常数出现突然增大的现象，通过分析发现该现象是由于界面价态不连续以及功函数差异造成的。本项目立足于铁电薄膜的微观结构，借助于像差校正透射电镜，发现了闭合畴的调控规律以及界面效应的影响，为铁电薄膜应用于铁电存储器提供了更多的基础科研理论结果。