功能化氧化物异质结界面的双球差电镜原位实时表征

Interfaces between complex oxides and electronic systems with unusual electronic properties can be fabricated. Recently, motivated by the discovery of a high-mobility two dimensional electron gas (2DEG) with high carrier density at heterointerfaces combining two band insulators LaAlO3 and SrTiO3 (LAO/STO), numerous electronic properties at such interface have been deeply investigated, revealing superconducting and intriguing magneto-transport properties. These significant results show that 2DEG at complex oxide interfaces have an enormous potential with scientific and technological impacts on future oxide nanoelectronic devices. In order to develop high performance devices using oxide 2DEG, it is imperative to functionalize the physical properties of 2DEG in a controllable way. One possible way is to integrate 2DEG with additional functional layers such as multifunctional oxide/LAO/STO heterostructure. In this proposal, we use a functionalized oxide 2DEG system integrating epitaxial ferroelectric Pb（ZnxTi1-x）O3 (PZT) thin films on LAO/STO as a model system. We will first employ various advanced imaging techniques: HAADF, holography and EELS with sub-?ngstr?m resolution on an double aberration-corrected S/TEM to extract the maximum quantitative information on localized atomic and electronic structure and charge distribution at the interfaces. We will then combine TEM imaging and novel in-situ scanning probe techniques to study the kinetics and dynamics of the metal-insulating transition of 2DEG during ferroelectric switching of the PZT overlayer at millisecond temporal and sub-?ngstr?m spatial resolution in epitaxial heterostructure of PZT on LAO/STO under applied electric field. This proposed experimental study will reveal fundamental mechanism of the non-volatile control of 2DEG conductivity at the conducting polar/nonpolar oxide heterointerface for the development of novel memory nanoelectronics.

为突破当今微电子器件的尺寸极限，发展新一代多功能、低功耗器件技术，材料物理界亟需开展复杂功能材料及其界面结构的设计、构造与人工调控原理和方法的基础研究。相对于传统半导体，氧化物材料具有更加丰富的物理性质以及更广泛的表面界面结构组态、化学成分、电子学输运性能的可调控性， 因此完全有希望替代半导体界面成为新一代器件的主角。要全面深入理解其中的新奇物理现象，就必须精确掌握氧化物异质界面在几个埃范围内电子结构和原子结构的变化，这种从亚原子尺度上对结构进行实时有效的观测和表征是极具挑战性的。面临这样的机遇与挑战, 基于申请人在高分辨电镜技术和应用方面深厚的积累，本申请提出发展和利用亚原子分辨成像和相关谱学分析技术，研究功能氧化物异质界面的组分、原子结构、局域晶格应变、电子特性，以及在外场作用下的演化规律，深入探索界面上二维电子气形成的物理机理及其调控规律, 为发展新型信息存储器件提供科学依据。

传统微电子工业的持续发展，依赖于器件功能单元的微型化和集成化， 目前已发展到接近摩尔定律的量子极限,人们亟需发展新型的电子器件。低维二维材料和氧化物界面体系不仅为凝聚态物理学的基础研究提供了丰富平台，还为面向新型电子器件设计的量子调控研究开拓出更为广阔的空间。本项目在原子尺度上研究了多种先进功能二维薄膜和氧化物异质结材料体系的原子结构和电子结构信息，揭示低维维材料和二维界面的电学性能及其它相关新奇现象的物理本质；在PZT/LAO/STO异质结构中，研究了铁电极化对界面导电性调控机理【ACS Applied Materials & Interfaces】。研究了引起LaMnO3外延薄膜体系反铁磁-铁磁转变现象的Mn离子变价机理【Advanced Electronic Materials】；研究了超薄BiFeO3铁电薄膜表面单原子层的铁电极化增强效应【Advanced Materials】；提出一种多态存储器件钙钛矿多铁异质结器件，阐述了多阻态调控的机理【Applied Physics Letters】。开发了基于电子全息的多功能超高分辨衍射成像方法，为材料提供了强有力的表征工具和手段，具有潜在的应用价值。提出了一种新的in-line的电子全息成像技术，实现了对亚原子分辨的轻元素的探测【Scientific Reports】，进一步拓展成了三维结构重构【Nature Communications】，有望成为具有高集成度的的高分辨成像方法【Phys. Rev. Lett.】上和申请国际专利【国际PCT/CN2018/108278】。发展了亚原子尺度原位实时电镜表征方法和手段,设计并开发了基于原位芯片的高稳定性光电原位测试平台，获得国家授权【2015104769008；2015104757585】，并在显微学顶刊【Ultramicroscopy】上发表。将该表征平台应用于多种氧化异质结系统中（PZT/LSMO, Graphene/MoOxS2-x/Graphene，BFO等）。揭示了该忆阻器中基于氧离子迁移的工作机制，成功解释了电子通道产生的机理【Nature Electronics】, 为新一代高密度非挥发信息存储器件提供重要的实验基础和理论依据。在国外期刊发表和已接收SCI论文43篇。申请国家发明专利5件，授权3件。申请国际发明专利1件。