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

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.