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

非技术概述日常使用的电子设备中存在的纳米材料应该经过设计，使设备变得更小，并增强其功能。要做到这一点，应该找到新的方法来收获这些材料的性能。一种方法是设计这些纳米材料中自然存在的原子级缺陷。虽然所有的晶态纳米材料都有各种各样的缺陷，但有些缺陷比其他的更有希望。一维缺陷，通常被称为线缺陷，只有几个原子宽，沿着整个晶体运行。这是一个绝佳的机会，让他们设计出想要的房产。由于它们只有几个原子宽，它们是嵌入主要材料中的耐人寻味的物体，它们可以具有独特的新的令人兴奋的性质。对这些线缺陷的研究需要具有能够探测这些缺陷的特性的超高分辨率显微镜。该项目使用专门的分析扫描电子显微镜来研究这些线缺陷的身份、性质和来源。将这些观察结果与理论预测相结合，将在表征缺陷时提供额外的灵活性。钙钛矿型氧化物薄膜已被证明是此类缺陷的极好宿主。这一结果不仅将影响钙钛矿晶体缺陷的科学研究，还将影响到新一代纳米材料工程的缺陷工程。在该项目的框架内，高中生将访问明尼苏达大学，以互动方式参观表征设施的电子显微镜中心，并观看高分辨率电子显微镜的实际操作。这项外展教育活动将是一项为期一年的学术计划。每年，来自当地高中的学生和教师团体都会参加这些旅游，其中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攻读技术学科。它还应该帮助教师利用他们在明尼苏达大学访问期间获得的图像，更好地向学生传达纳米材料和显微镜背后的科学知识。技术概述过去二十年的进展表明，当大量材料具有纳米尺度的尺寸时，它们在科学上是令人兴奋的，在技术上也是可取的。对纳米材料独有的新现象的发现几乎每天都在进行，从新的物理学--例如半导体纳米线中量子比特的量子输运或作为拓扑绝缘体的硫化物--到新的应用。识别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产生的缺陷，特别是延伸的缺陷，有可能为令人兴奋的新科学和下一代技术开辟一条新的道路。这些延伸线(或1D、位错和错位等)和平面(或2D、晶界、层错等)缺陷特别有希望，因为它们在一个或两个方向上横跨整个晶体，在其他方向上原子上很小。其中，线缺陷在两个方向上只有几个原子宽，在第三个方向上扩展。在这种自然的几何结构下，人们预计一维缺陷的性质应该类似于原子链或单单元单元链。这些缺陷应该富含2D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利用缺陷和宿主的特征。对新缺陷的研究--了解它们的特性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步。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的形成及其重排的影响是这项工作的中心目标。钙钛矿氧化物(ABO3)，由于其复杂的结构，具有高度的柔韧性，可以适应各种类型的扭曲。这种结构灵活性允许钙钛矿主体适应独特的扩展缺陷，包括那些不同成分的缺陷。因此，探索钙钛矿氧化物中的这种非常规缺陷有可能取得极其丰硕的成果，极大地扩展陶瓷晶体的基础科学，并改变下一代纳米材料。这项关于钙钛矿氧化物中非常规一维线缺陷的研究将使用原子分辨率、分析性扫描电子显微镜(STEM)和密度泛函(DFT)计算进行异地和原位研究。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.