Image Contrast in Atomic Resolution STEM

原子分辨率 STEM 中的图像对比度

• 批准号: 0804631
• 负责人: Susanne Stemmer
• 金额: $ 36万
• 依托单位: University of California-Santa Barbara
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-06-15 至 2012-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0804631&HistoricalAwards=false
• 关键词: Image; Contrast; Atomic; Resolution; STEM

Technical: This project aims to gain a quantitative understanding of the chemical contrast in atomic resolution scanning transmission electron microscopy (STEM) with the ultimate objective of achieving a comprehensive knowledge of defects and interfaces in solids. High-angle annular dark-field (HAADF or Z-contrast) imaging in STEM has been recognized as a technique that provides atomic structure images with chemical sensitivity. A quantitative understanding of the atomic number contrast in these images would allow for analysis of impurity or dopant atoms near interfaces and defects with atomic-level spatial resolution. Despite the significant progress that has been made over the last decade in the theory of STEM Z-contrast imaging a significant mismatch exists between predictions of image contrast made by theory and that of experimental images. While this discrepancy does not affect the interpretation of images of perfect crystals, it precludes a quantitative, atomic-scale chemical analysis of defects and interfaces. In this project, the physical origins of the disagreement between theory and experiments will be investigated in a systematic series of experiments designed to distinguish between contributions from instrumental, environmental and sample effects and those related to the scattering physics of high-energy electrons. In particular, the influence of temperature (phonon scattering), sample thickness, acceleration voltage, convergence angle, inelastic scattering, sample surface layers, point defects, and atom displacements on the image contrast will be examined. The experimental findings will be compared with simulation results, in collaboration with scientists at the University of Melbourne.Non-technical: The project addresses basic research issues in a topical area of materials science with high technological relevance, and is expected to provide new scientific knowledge of structure and chemistry at the atomic scale, which is critical for advances in modern materials science and nanotechnology. The project will contribute to the interdisciplinary and international training of graduate students. Through collaboration with theorists in Australia, the students supported by the program will learn about the latest developments in theory, bridge the gap between applied and fundamental materials research, learn a broad range of scientific methods, and become trained in international collaboration. The project also offers two- to three-month-long, self-contained internships for undergraduate students. Results obtained in this project will be used to develop teaching modules for a web-based Electron Microscopy Database (EMdb) on the topic of quantitatively analyzing chemical contrast in atomic resolution imaging.

技术：该项目旨在定量了解原子分辨率扫描透射电子显微镜 (STEM) 中的化学对比度，最终目标是全面了解固体中的缺陷和界面。 STEM 中的高角度环形暗场（HAADF 或 Z 对比度）成像已被认为是一种提供具有化学敏感性的原子结构图像的技术。对这些图像中原子序数对比的定量理解将允许以原子级空间分辨率分析界面和缺陷附近的杂质或掺杂剂原子。尽管 STEM Z 对比度成像理论在过去十年中取得了重大进展，但理论预测的图像对比度与实验图像的预测之间存在显着的不匹配。虽然这种差异不会影响对完美晶体图像的解释，但它妨碍了对缺陷和界面进行定量、原子级化学分析。在这个项目中，理论与实验之间不一致的物理根源将通过一系列系统实验来研究，这些实验旨在区分仪器、环境和样品效应的贡献以及与高能电子散射物理相关的贡献。特别是，将检查温度（声子散射）、样品厚度、加速电压、会聚角、非弹性散射、样品表面层、点缺陷和原子位移对图像对比度的影响。与墨尔本大学的科学家合作，将实验结果与模拟结果进行比较。 非技术性：该项目解决具有高度技术相关性的材料科学主题领域的基础研究问题，预计将提供新的科学知识原子尺度的结构和化学，这对于现代材料科学和纳米技术的进步至关重要。该项目将有助于研究生的跨学科和国际化培训。通过与澳大利亚理论家的合作，该项目支持的学生将了解理论的最新发展，弥合应用和基础材料研究之间的差距，学习广泛的科学方法，并接受国际合作的培训。该项目还为本科生提供为期两到三个月的独立实习机会。该项目获得的结果将用于开发基于网络的电子显微镜数据库（EMdb）的教学模块，其主题是定量分析原子分辨率成像中的化学对比度。