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往往取决于设备的稳定性和耐用性--S活性元件材料。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下降，或者在宏观层面上完全失效。然而，与此同时，未来的一些应用实际上会依靠这些原子级缺陷和接口的存在来提高设备的性能？S。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一种材料的影响？S的性质，我们可以在宏观层面上提高材料的功能。因此，基本了解原子尺度的缺陷或界面如何影响材料？S的宏观行为对于继续开发可靠的下一代设备至关重要。钴氧化物是近年来引起科学关注的一类陶瓷材料，它是一种廉价、无毒、高度稳定的化合物，具有超导、热电或磁阻等性能。这些特性使钴氧化物在广泛的新设备应用中具有吸引力。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，而它们的热电性能可能会导致涂层的开发，使汽车排气管或炉膛排气管产生的热量能够转化为电能。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，因为缺乏对原子层面上材料正在发生的事情的基本了解。这项职业资助利用原子分辨率扫描电子显微镜和电子能量损失谱(EELS)相结合的方法来研究控制氧化钴陶瓷磁性和电学性能的基本机制，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，特别是代表不足的少数群体，进行最先进的材料表征方面的培训。将为本科生制定暑期计划，并将通过芝加哥伊利诺伊大学的皮？S本科生研究杂志进一步培养本科生对研究项目的参与。技术描述：本职业计划的目标是研究电荷、轨道和自旋相互作用如何影响混价钴氧化物陶瓷的磁性和电子结构。将研究两个系统：LaCoO_3和Ca3Co_4O_9。这些体系之所以被选中，是因为它们具有耐人寻味的、潜在的广泛用途，以及它们作为其他强相关钴氧化物陶瓷的模型结构的地位。LaCoO_3表现出磁输运性质和两个自旋态转变，导致磁性相变而没有任何结构转变，而失配层状Ca3Co4O_9显示出异常高的热功率。利用扫描电子显微镜(STEM)中的原子分辨Z衬度成像技术(EELS)和原位加热/冷却实验(10T-1000K)研究了这些材料的局域原子和电子结构。皮？S实验室装置包括一台像差校正的STEM，它将实现亚空间分辨率和亚EV能量分辨率，以及一台用于原子分辨率原位加热和冷却实验的常规瞬变/STEM。现场STEM分析将得到MBE薄膜合成、宏观磁化、输运测量、表面表征以及第一性原理建模的支持。这种实验和理论相结合的方法能够揭示混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，这将推动电子陶瓷领域的发展，并导致发现可用作创新器件和传感器的新现象。该项目的一个重要特点是通过培养尖端的透射电子显微镜和理论材料科学的本科生和研究生来整合研究和教育。

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.