表界面原子结构的同步辐射衍射表征技术及其应用

Along with the development of surface and interface physics of materials, it is urgent to understand the structure-property relationship at the atomic level. However, absence of appropriate structural analysis technique has limited the works performed in China. For this reason, this project aims to develop advanced surface x-ray diffraction technique – CTR/COBRA at Shanghai Synchrotron Radiation Facility. After that, series of demonstration researches shall be performed based on it. The research contents include: 1) measurement of 1D- and 3D-CTR signals with linear and area detector respectively, signal correction, linkage control of filterbox and detector, and reduction of background signal and detector noise; 2) Optimizing the algorithms and processes of COBRA, developing a graphic user interface, and obtaining reliable electron density information from the CTR signals; 3) taking the typical two-dimensional interfaces between transition-metal oxides for example, such as interface of LaVO3/SrTiO3, probing the atomic structure of the interfaces with CTR/COBRA, combined with PPMS, SQUID, XMCD measurements for physical properties, to reveal the relationship between the interfacial properties (magnetic or quantum electric transport) and the microstructure (lattice distortion or octahedral rotation). The implementation of this project will provide techniques for the domestic synchrotron surface x-ray diffraction stations under construction or in-plan. Also, this project will arm the domestic surface and interface studies with powerful tools, and promote them to the atomic-level of control.

表界面材料物理的深入研究迫切需要从原子层次理解表面/界面微观结构对其物性调控的机理，然而，结构表征技术的缺乏限制了国内工作的开展。鉴于此，本项目拟在上海同步辐射装置上发展先进的X射线表面衍射技术CTR/COBRA并开展示例性研究工作，包括：采用线探/面探高效采集一维/三维CTR衍射信号，解决背底噪声抑制、信号校正、软硬件联动控制等问题，获取高信噪比信号；优化COBRA解析算法和流程，实现操作界面可视化，从CTR信号解析出可靠电子密度信息；以LaVO3/SrTiO3等典型过渡金属氧化物二维界面体系为例，采用CTR/COBRA获取界面的原子结构，结合PPMS、SQUID、XMCD表征物性，揭示其界面量子输运、磁性等物性与晶格畸变、氧八面体旋转等微观结构的关联。本项目的开展将为国内正在或即将建设的同步辐射表面衍射站做好技术准备，为相关表界面研究提供强大表征手段，推动其向原子级精细控制层次发展。

表界面材料物理的深入研究迫切需要从原子层次理解表面/界面微观结构对其物性调控的机理，然而，结构表征技术的缺乏限制了国内工作的开展。本项目在上海同步辐射装置的衍射站14B上发展了CTR/COBRA表面衍射技术，通过优化机械设计和控制，并采用二维低噪高动态范围X射线探测器，采集到了信噪比较高的CTR信号，并最终实现了薄膜法向电子密度的解析，分辨率达0.027nm。运用同步辐射表面衍射技术，成功揭示了多个薄膜材料体系的微观结构与其宏观物性的关联：1）揭示了NdNiO3/NdGaO3超薄外延薄膜中异常MIT行为的结构起源；2）利用同步辐射原位研究了NdNiO3/NdGaO3外延薄膜在离子液体调控下的微观结构和价态演化，探讨了离子液体调控的本质；3）用紫外激光调控CoFe2O4表面氧空位以增强其析氧反应催化活性；4）利用同步辐射原位变温衍射揭示了BiFeO3铁电畴随温度的各向异性演化；5）用Laser Pump -X-ray Probe技术研究BiFeO3薄膜（T’/R’+T相）相转变的动态过程，证实铁电/多铁中的多畴/相体系可以通过光致相变实现纳秒时间尺度的结构调控；6）发现了PbTiO3/DyScO3外延薄膜中各向异性的铁弹畴结构；7）揭示了应变调控VO2薄膜金属-绝缘体转变的根源；8）研究温度气氛对SrVOx晶相和物性的调控，发现SrVO3和Sr2V2O7之间的可逆转变；9）研究了纳米铁磁绝缘体(1-x)LaMnO3:xNiO薄膜的晶体结构和价态；10）研究并揭示了几种铁电或多铁自支撑薄膜(BTO、BFO、Fe/BTO)的晶体结构和畴结构。以上研究工作在Appl.Phys.Lett., Phys.Rev.B, Advanced Materials Interface, Science等期刊发表论文21篇; 在重要学术会议上做口头报告交流6次；培养博士4名，硕士2名；申请并授权发明专利2项。