铋系层状钙钛矿多铁体的分子束外延生长及多场耦合效应研究

Multiferroic (MF) materials with bismuth layered perovskite show their potential application in magnetoelectric (ME) devices because of the room-temperature multiferroic properties and robust ME coupling. However, the inherent relationship between ME coupling and cation distributions at B sites is still needed further clarification. In this project, molecular beam epitaxy (MBE) technique, by which surficial and/or interfacial structures can be preciously controlled and atomic layer growth mode can be achieved, is employed to grow the MF materials with bismuth layered perovskite. Moreover, reflection high energy electron diffraction (RHEED) is utilized to monitor in situ the growth processes, including the oscillation of the intensity of the RHEED fringe and the surface reconstruction phenomena. Through the above technique routes, alternating epitaxial growth mode of the TiO, FeO and BiO sub-atomic layers is expected to be realized, and the epitaxial growth kinetics will be built. Based the above-built growth modes, single crystal thin films with different microstructures and interfaces, as well as superlattices are further grown by adjusting the Ionic Order Degree (IOD) at B sites, the layer number of the ion oxygen octahedrons and the cation distributions at B site. And then we systematically study the electrical, magnetic and optical properties of the grown films employing dielectric and ferroelectric analyzer, piezoelectric force microscopy (PFM), physical property measurement system (PPMS), Raman, transmittance and infrared reflection spectrum techniques and so on at different temperatures. Therefore, we will obtain the effects of the IOD and the cation distributions at B sites on the electronic and magnetic structures, electronic energy band structure, polarization and magnetization etc, and the origin of magnetic properties and the mechanism of ME coupling are tried to be clarified. Finally, we try to explore some new phenomena induced by the charge and spin reconstruction, and lattice distortion occurred at interfaces. Through this project, the kinetics of the epitaxial growth of the oxide superlattices will be built, and the theoretical and technical development of oxide superlattices will be promoted.

铋系层状钙钛矿多铁氧化物具有室温多铁性和强耦合特性，展示其在磁电器件的应用潜力，但其磁电耦合与B位离子分布状态的内在关联机理仍不清楚。本项目拟采用能够精确控制表面/界面结构、实现原子层调控生长的分子束外延技术制备铋系层状多铁体；利用原位反射高能电子衍射监控衍射条纹强度的振荡和表面重构，实现TiO、FeO、BiO亚原子层的交替外延生长并获得其生长动力学规律；进而调控B位有序度、铁氧八面体层数与空间分布状态，构建不同微结构和界面状态的单晶薄膜和超晶格；在此基础上，系统研究该类体系在多场（温度场、电场、磁场、光场）作用下的电、磁和光学特性，建立B位有序度和分布状态对体系电磁结构、电子能带结构、铁电极化与磁极化的调控规律，弄清磁性起源的本源及磁电耦合的微观机制；并探索界面电荷与自旋重构及晶格畸变所诱导的新效应。通过本项目的研究拟建立氧化物超晶格外延的动力学规律，推动氧化物超晶格的理论和技术发展。

铋系层状钙钛矿多铁氧化物具有室温多铁性和强耦合特性，展示其在磁电耦合器件的巨大应用潜力。本项目主要围绕如下研究内容展开，涵盖了（1）单晶薄膜与异质结如铁电、多铁性及半导体的分子束外延MBE生长与外延工艺优化，尤其聚焦基于原位反射高能电子衍射（RHEED）辅助技术实现了Sr-O，Ti-O和Mn-O亚晶格的逐层交替MBE外延生长，总结出单晶薄膜与异质结的分子束外延MBE生长动力学规律；（2）多铁性材料中缺陷产生机制、铁电畴翻转机理、以及载流子/缺陷相关的弛豫和输运机制；（3）自旋序对铁电极化状态的影响规律，铁性材料中元激发以及电子跃迁行为的揭示；（4）研制了若干原型器件开发其在光电探测器和气敏传感器的应用。在项目执行过程中，成功制备了一系列铋系Aurivillius层状Bi5Ti3FeO15、SrTiO3、SrMnO3以及CdTe与MnTe等多铁体/半导体单晶薄膜与异质结。掌握了亚晶格（如Sr-O，Ti-O和Mn-O亚晶格）交替生长与分子束共沉积生长等能够精确控制表面/界面结构、实现原子层调控生长的分子束外延MBE技术；获得了薄膜/衬底、晶粒/晶界和薄膜/电极等界面微纳结构对外延成膜与质量、光谱学性质、界面势垒、铁电畴结构、介电响应及栅极调控能力等的影响规律；在铋系层状Aurivillius多铁体，强关联电子体系SrMnO3及铁磁/铁电异质结等干铁性体系中建立了自旋序对铁电极化的作用机理，以及氧空位、变价离子等缺陷/缺陷偶极子的介电弛豫和输运机制；获得了铋系层状Aurivillius多铁体中各向异性相关的畴结构和畴反转行为及其钙钛矿Fe-O层靠近或远离Bi-O层对磁性和磁电耦合的影响规律；通过介电频谱揭示SrMnO3外延单晶薄膜中氧空位与Jahn-Teller小极化子之间的内在关联；揭示出若干铁性体系中电—声耦合、铁电极化子元激发产生及输运动力学规律；利用共生长技术实现了CdTe和MnTe高质量单晶薄膜的MBE大失配与范德华外延生长，并研制出可应用于光电探测器的原型光电子器件。通过本项目的研究建立了氧化物单晶薄膜与异质结的外延动力学规律，有助于推动氧化物分子束外延的理论和技术发展。