{'fraction_non_alphanumeric': 0.024829298572315334, 'fraction_numerical': 0.004965859714463066, 'mean_word_length': 5.526315789473684, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Three-Dimensional Imaging of Point Defects in Functional Materials Using Quantitative STEM

Many important properties of nanoscale functional and energy-related materials are determined by individual point defects, such as impurity dopant atoms and vacancies. Therefore, to understand the materials physics and exploit the properties of emerging materials, it is crucial to precisely determine the 3D location, distribution, segregation, pairing, and clustering of point defects. Electron microscopy has been previously used to identify individual point defects. For example, annular dark-field (ADF) imaging in STEM is sensitive to the atomic number of the material, and therefore can provide intuitive information on the lateral positions of the impurity atoms [1]. To complete the 3D information, however, the precise depth location (the direction parallel to the electron beam) of the point defects must be uncovered as well. However, acquiring depth information at the atomic scale is challenging. Even with high probe convergence angles, the depth resolution of STEM remains above ~10 nm [2], which makes it difficult to determine the 3D position of point defects using conventional approaches, such as focal series reconstruction or confocal microscopy. These conventional techniques also require the acquisition of multiple images of the same area of the sample, and therefore may suffer from low precision due to sample drift, or radiation damage due to long beam exposure. The development of a 3D electron microscopy technique that combines resolution, precision, and efficiency is therefore required.