CAREER: Atomic-Resolution Study of Electron-Spin Interaction in Strongly-Correlated Mixed-Valence Cobalt Oxide Nano-Structures

非技术描述：许多电子设备的性能和可靠性通常取决于设备的稳定性和耐用性。的活性成分材料。例如，原子级结构缺陷或不同材料之间的界面通常会导致器件性能降低，或宏观层面的完全失效。然而，与此同时，未来的一些应用实际上将依赖于这些原子级缺陷和界面的存在来改进器件？的表现。这些缺陷和界面是不可避免的，但通过了解如何控制和操纵它们对材料的影响？的性质，我们可以在宏观层面上提高材料的功能性。因此，对原子级缺陷或界面如何影响材料的基本理解？的宏观行为对于继续开发可靠的下一代器件至关重要。 钴氧化物是一类陶瓷材料，其最近作为具有诸如超导性、热电行为或磁阻行为的特性的廉价、无毒且高度稳定的化合物组而引起科学关注。 这些特性使得钴氧化物在广泛的新器件应用中具有吸引力。例如，钴氧化物的磁性有可能彻底改变高容量固态计算机硬盘驱动器中的磁存储，而它们的热电特性可能导致涂层的发展，从而允许汽车排气管或炉排气管的热量转化为电力。然而，目前，钴氧化物对于可行的宏观应用来说既不可靠也不够有效，因为缺乏对原子水平上材料发生的事情的基本理解。 这项CAREER资助利用原子分辨率扫描透射电子显微镜结合电子能量损失谱（EELS）来研究钴氧化物陶瓷的磁和电性能的基本机制以及缺陷和界面对这些性能的影响。 这项建议的教育方面涉及对本科生和研究生，特别是代表性不足的少数民族学生进行最新材料表征方面的培训。将开发本科生暑期课程，并通过PI进一步促进本科生参与研究项目。技术描述：本CAREER提案的目的是研究电荷、轨道和自旋相互作用如何影响混合价态钴氧化物陶瓷的磁性和电子结构。两个系统将被检查：LaCoO 3和Ca 3Co 4 O 9。选择这些系统是因为它们有趣的，潜在的广泛有用的特性，以及它们作为其他强相关的钴氧化物陶瓷的模型结构的地位。LaCoO 3具有磁输运性质以及两个自旋态转变，导致磁相变而没有任何结构转变，而错配层Ca 3Co 4 O 9则表现出异常高的热功率。原子分辨率Z衬度成像扫描透射电子显微镜（STEM）（EELS）和原位加热/冷却实验（10 T 1000 K）被用来研究这些材料的局部原子和电子结构。私家侦探？的实验室设置包括一个像差校正的干，这将允许亚电子伏特的空间分辨率和亚电子伏特的能量分辨率，以及一个传统的TEM/干原子分辨率原位加热和冷却实验。原位STEM分析将得到MBE薄膜合成、宏观磁化、传输测量和表面表征以及第一原理建模的支持。这种实验和理论技术的结合使混合价钴氧化物陶瓷中电荷，轨道和自旋相互作用的基本结构-性质关系得以解开，这可以推进电子陶瓷领域，并导致发现可用作创新器件和传感器的涌现现象。该计划的一个重要特点是通过培养尖端透射电子显微镜和理论材料科学的本科生和研究生，实现研究与教育的融合。

NON-TECHNICAL DESCRIPTION: The performance and reliability of many electronic devices is frequently governed by the stability and durability of the device?s active component materials. For example, atomic level structural defects, or interfaces between different materials often cause decreases in device performance, or total failure at a macro level. At the same time, however, some future applications will actually rely on the presence of these atomic level defects and interfaces to improve the device?s performance. These defects and interfaces are unavoidable, but by understanding how to control and manipulate their influence on a material?s properties, we can improve the functionality of the material on the macro level. Accordingly, a fundamental understanding of how atomic-scale defects or interfaces influence a material?s macroscopic behavior is essential to continuing the development of reliable, next generation devices. Cobalt oxides are one class of ceramic materials that has recently attracted scientific attention as an inexpensive, non-toxic, and highly stabile group of compounds with properties such as superconductivity, thermo-electric behavior, or magneto-resistive behavior. These properties make cobalt oxides attractive for use in a wide range of new device applications. For example, the magnetic properties of cobalt oxides have the potential to revolutionize magnetic storage in high capacity solid-state computer hard-drives, while their thermo-electric properties may lead to the development of coatings that will allow heat from automotive tailpipes or furnace exhaust pipes to be converted into electricity. At present, however, cobalt oxides are neither reliable nor efficient enough for viable macroscopic applications, because there is a lack a fundamental understanding of what is happening with the material on the atomic-level. This CAREER grant utilizes atomic-resolution scanning transmission electron microscopy combined with electron energy-loss spectroscopy (EELS) to investigate the fundamental mechanisms governing the magnetic and electrical properties of cobalt-oxide ceramics and the effects of defects and interfaces on these properties. The educational aspect of this proposal involves training of undergraduate and graduate students, in particular underrepresented minorities, in state-of-the-art materials characterization. Summer programs for undergraduate students will be developed, and the participation of undergraduate students in research projects will be fostered further through the PI?s Journal of Undergraduate Research at the University of Illinois at Chicago.TECHNICAL DESCRIPTION: The objective of this CAREER proposal is to examine how charge, orbital and spin-interactions influence the magnetic and electronic structures of mixed-valence cobalt-oxide ceramics. Two systems will be examined: LaCoO3 and Ca3Co4O9. These systems were chosen for their intriguing, potentially widely useful properties, and for their status as model structures for other strongly correlated cobalt-oxide ceramics. LaCoO3 exhibits magneto-transport properties as well as two spin-state transitions that result in magnetic phase transitions without any structural transition, while the misfit-layered Ca3Co4O9 shows an exceptionally high thermo-power. Atomic-resolution Z-contrast imaging in a scanning transmission electron microscope (STEM) with (EELS) and in-situ heating/cooling experiments (10 T 1000 K) is being used to study the local atomic and electronic structures of these materials. The PI?s laboratory setup includes an aberration-corrected STEM, which will allow for sub-Å spatial-resolution and sub-eV energy-resolution, as well as a conventional TEM/STEM for atomic-resolution insitu heating and cooling experiments. The insitu STEM analysis will be supported by MBE thinfilm synthesis, macroscopic magnetization, transport measurements, and surface characterization, as well as first principles modeling. This combination of experimental and theoretical techniques enables the fundamental structure-properties relationship of charge, orbital and spin-interactions in mixed-valence cobalt-oxide ceramics to be unraveled, which could advance the field of electro-ceramics and lead to the discovery of emergent phenomena that can be used as innovative devices and sensors. An important feature of this program is the integration of research and education through the training of undergraduate and graduate students in cutting-edge transmission electron microscopy and theoretical materials science.