In-situ and ex-situ STEM study of non-conventional line defects in perovskite oxides

日常使用的电子设备中的纳米级材料应该被设计成使设备更小并增加其功能。要做到这一点，就必须找到新的方法来获取这些材料的特性。一种方法是设计这些纳米材料中自然存在的原子级缺陷。虽然所有的晶体纳米材料都有各种各样的缺陷，但有些缺陷比其他缺陷更有前途。一维缺陷，通常被称为线缺陷，只有几个原子宽，并沿着整个晶体运行。这是一个绝好的机会来设计他们，让他们得到想要的属性。由于它们只有几个原子那么大，所以它们是嵌在主要材料中的有趣物体，而且它们可以具有独特的、令人兴奋的新特性。研究这些线缺陷需要超高分辨率显微镜，其特征可以探测这些缺陷的性质。本项目采用专门的分析扫描透射电子显微镜来研究这些线缺陷的特征、性质和起源。将这些观察结果与理论预测相结合，将在描述缺陷时提供额外的灵活性。钙钛矿氧化物薄膜已被证明是这种缺陷的优良宿主。研究结果不仅将影响钙钛矿晶体缺陷的研究，而且将影响缺陷工程的下一代纳米材料工程。在这个项目的框架内，高中生将访问明尼苏达大学，在表征设施的电子显微镜中心进行互动参观，并看到高分辨率电子显微镜的作用。这项外展教育活动将是一个为期一年的学术项目。每年，来自当地高中的学生和教师团体将参加这些参观活动，包括有相当多少数民族学生的学校。这种对材料结构和先进电子显微镜操作的实时深入研究，应该会激励学生在大学里学习技术学科。它还应该帮助教师更好地向学生传达纳米材料和显微镜背后的科学知识，并使用他们在明尼苏达大学访问期间获得的图像。技术摘要过去二十年的进展表明，当大量材料具有纳米尺度时，它们在科学上是令人兴奋的，在技术上是可取的。几乎每天都在发现纳米材料特有的新现象，从新的物理现象——比如半导体纳米线中量子比特的量子传输，或者作为拓扑绝缘体的硫族四烯矿——到新的应用。确定纳米材料的下一个前沿变得越来越重要。通过探索和设计纳米材料中自然存在的缺陷，特别是扩展缺陷，可以为令人兴奋的新科学和下一代技术提供新的途径。这些延长线（或一维，位错和位错等）和平面（或二维，晶界，堆积缺陷等）缺陷特别有希望，因为它们在一个或两个方向上贯穿整个晶体，并且在其他方向上原子小。其中，线缺陷在两个方向上只有几个原子宽，在第三个方向上延伸。有了这样的自然几何结构，预计一维缺陷的性质应该类似于原子链或单单元细胞链。这些缺陷应该富含二维材料中没有的新物理和新量子材料现象。含有它们的纳米结构可以同时利用缺陷和宿主的特征。对新缺陷的研究——了解它们的性质并将它们设计成新的结构——是这个项目的主要主题，它可能是纳米材料的下一个方向。确定关键因素（如成分、应变和温度）对钙钛矿氧化物中线缺陷形成及其重排的影响是本工作的中心目标。钙钛矿氧化物（ABO3）由于其复杂的结构，具有高度的灵活性，可以适应各种类型的扭曲。这种结构的灵活性使得钙钛矿主体能够容纳独特的扩展缺陷，包括那些不同成分的缺陷。因此，在钙钛矿氧化物中探索这种非常规缺陷具有非常富有成效的潜力，在很大程度上扩展了陶瓷晶体的基础科学，并改变了下一代纳米材料。本研究将利用原子分辨率、分析扫描透射电子显微镜（STEM）和密度函数特罗伊（DFT）计算辅助，对钙钛矿氧化物中的非常规一维线缺陷进行原位和原位研究。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-Technical Summary The nanoscale materials present in electronic devices used every day should be engineered to make the devices smaller and increase their functions. To do this, new ways to harvest the properties of these materials should be found. One route is engineering atomic-level defects naturally present in these nanomaterials. While all crystalline nanomaterials have variety of defects in them, some defects are more promising than others. One dimensional defects, often referred to as line defects, are only a-few-atoms-wide and run along the entire crystal. This is an excellent opportunity to engineer them to get the properties wanted. Since they are only a-few-atoms-wide, they are intriguing objects embedded inside the main material, and they can have new and exciting properties that are unique to them. Study of these line defects requires ultra-high-resolution microscopes with features that can probe the properties of these defects. This project employs specialized analytical scanning transmission electron microscopes to study the identities, properties, and origins of these line defects. Combining these observations with theoretical predictions will provide additional flexibility when characterizing the defects. Perovskite oxide thin films have proven to be excellent hosts for such defects. The results will affect not only the science of defects in perovskite crystals, but also affect next-generation nanomaterial engineering by defect engineering. Within the framework of this project, high-school students will visit the University of Minnesota to have interactive tours of the Electron Microscopy Center at the Characterization Facility and see high-resolution electron microscopes in action. This outreach educational activity will be an academic-year-long program. Each year, groups of students and teachers from local high schools will participate in these tours, including schools with a considerable minority student population. Such a real-time dive into the structure of the materials and the operations of advanced electron microscopes should inspire students to pursue technical disciplines in college. It should also help teachers better convey to their students the science behind nanomaterials and microscopes using images obtained during their University of Minnesota visit. Technical SummaryAdvances over the past two decades have shown large numbers of materials can be scientifically exciting and technologically desirable when they have dimensions at the nanometer scale. Discoveries of new phenomena unique to nanoscale materials are being made almost daily, ranging from new physics—such as quantum transport of qubits in semiconductor nanowires or tetradymite chalcogenides being topological insulators—to new applications. Identifying the next frontiers in nanomaterials becomes more-and-more relevant. A new path for exciting new science and next-generation technology is possible through exploring and engineering the naturally-occurring defects in nanoscale materials, especially extended defects. These extended line (or 1D, dislocations and disclination, etc.) and planar (or 2D, grain boundaries, stacking faults, etc.) defects are particularly promising because they run across the entire crystal in one or two directions and are atomically small in other directions. Among them, line defects are only a-few-atoms-wide in two directions and extended in the third direction. With such natural geometry, it is expected that the properties of 1D defects should resemble a chain of atoms or a chain of single-unit cells. These defects should be rich with new physics and new quantum materials’ phenomena not seen in 2D materials. Nanostructures containing them could take advantage of both the features of the defect and the host. The study of new defects – understanding their properties and engineering them into new structures – is the main topic of this project, and it could be what is next in nanomaterials. Determining the effects of key factors (such as composition, strain, and temperature) on formation of line defects and their rearrangements in perovskite oxides are central aims of this work. Perovskite oxides (ABO3), are highly flexible and can accommodate various types of distortions, due to their complex structure. Such structural flexibility allows the perovskite host to accommodate unique extended defects, including those of different compositions. Thus, exploring such non-conventional defects in perovskite oxides has the potential to be extremely fruitful, largely expand the fundamental science of ceramic crystals, and transform next-generation nanomaterials. This study of non-conventional 1D line defects in perovskite oxides will be conducted ex-situ and in-situ using atomic-resolution, analytical scanning transmission electron microscopy (STEM) aided by density function tehroy (DFT) calculations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.