自组装氧化物薄膜的可控生长与多铁性研究

Because of their multifuctionalities and potential applications, self-assembled oxide thin films have attracted much attention from both the academic and industrial communities. Nowadays there are lots of experimental and theoretical works on the self-assembled oxide thin films. While the physical process underlying the self-assembly is fundamentally important yet poorly understood. And the controllable ordered nanostructures are quite lacking. The central challenge is to achieve a controllable self-assembly in oxide thin films. This is the main drawback which limited the application of self-assembled oxide thin films. In the present work, we are going to (1) fabricate composite thin films based on the SrMnO3 materials, investigate the process of self-assembly using the phase-separation theory, analyze how to manipulate the ordered nanostructures, and then understand the mechanism of self-assembly; (2) investigate the spin-phonon-strain coupling based on the measurements of magnetic, electrical, and magnetoelectric properties, understand the relationship between the microstructure and physical properties; (3) realize the controllable self-assembly in oxide thin films based on the manipulation of process, microstructures, and physical properties; (4) try to transform the SrMnO3 to be ferromagnetic-ferroelectric using the controllable ordered nanostructures and then investigate the possible magnetoelectric coupling in the composite thin films. We expect that our work will lead to a deeper understanding on the self-assembly mechanism. The main goal is to solve the key problem on the investigation of self-assembled oxide thin films and to establish the foundation of their potential applications.

自组装氧化物薄膜，由于其多功能性与应用前景，引起研究人员的广泛关注。现在虽然已经有一系列实验和理论的工作对其进行研究，但离自组装本质规律的理解与有序结构的可控生长还有非常长的距离，其核心问题是如何实现可控的自组装。本项目围绕这个核心问题，具体研究内容涵括四个方面：(1)通过制备基于SrMnO3材料的复合薄膜，研究相分离驱动自组装的过程和有序结构的调控规律，加深对自组装机理的理解；(2)通过测量复合薄膜的电、磁以及磁电耦合性质，研究SrMnO3中自旋-声子-应变之间的耦合关系，深入理解结构对物理性质的影响机制；(3)通过自组装过程、结构和物性的调控，实现可控的氧化物薄膜自组装；(4)通过有序结构的可控生长，在SrMnO3上施加足够强的应变，将其调制成铁磁、铁电共存且存在磁电耦合的多铁性材料。本项目工作将解决自组装氧化物薄膜研究的核心问题，为其实际应用奠定基础。

自组装氧化物薄膜，由于其多功能性与应用前景，引起研究人员的广泛关注。本项目以基于SrMnO3和BaTiO3的复合薄膜为例，理解氧化物薄膜自组装的本质规律，尝试有序结构的可控生长，并研究复合薄膜的电、磁性质。主要进展如下：.1. SrMnO3:MgO复合薄膜的制备与电、磁性质研究。通过XRD, TEM, STEM等测试手段发现，复合薄膜中SrMnO3与MgO两相分离，且分别以纳米团簇的形式存在。通过测量介电常数随温度变化曲线，发现在300-350K有明显峰值，说明其中存在从顺电到铁电的相变。同时，在室温测量到明显的MH loop，说明复合薄膜在室温有明显磁性；进一步，用高温SQUID测量发现，薄膜的铁磁居里温度远远高于室温，达到了约850K。.2. BaTiO3:Sm2O3复合薄膜的制备与电性质研究。复合薄膜中BaTiO3与SmO两相分离，且存在垂直方向的纳米有序结构。通过漏电电流测试发现，(111)取向Nb-STO上生长的复合薄膜，其漏电电流密度比(001) 取向Nb-STO上生长复合薄膜漏电流密度低2个量级，比(111)取向Nb-STO上生长的单相BTO薄膜漏电流密度低3个量级。通过分析发现，BTO与SmO两相之间“干净的”、无错配位错的垂直界面，正是复合薄膜中低漏电流密度与欧姆行为出现的主要原因。.3. 柔性复合薄膜BaTiO3:Sm2O3的负压力效应及其物性研究。使用脉冲激光沉积法在云母基底上生长了以SrTiO3为缓冲层，SrRuO3为导电层的BaTiO3:Sm2O3复合薄膜。这种柔性基底不但使得Sm2O3相对BTO相产生了负压力，对其晶格产生了明显的拉伸应变从而提高了其铁电居里温度、铁电性能、压电性能，而且使其具有柔韧可弯曲的能力，使其成为柔性传感器的候选材料。.项目共发表论文33篇，包括APL 3篇，ACS Appl. Mater. & Inter. 3篇，应邀综述文章两篇。共培养博士生2名、硕士生2名，其中2名硕士生和1名博士生已经毕业。