Spatial and Temporal Fluctuations in Coherent Electron Nanodiffraction from Metallic Glasses and Glass-forming Liquids

本项目支持在扫描透射电子显微镜中使用系统相干电子纳米衍射技术（称为波动电子显微镜技术）对金属玻璃和金属玻璃形成液体的结构和原子动力学进行研究。 时间分辨的纳米衍射实验作为温度的函数将测试的假设，即金属玻璃形成液体表现出空间的非均匀动力学，发挥其玻璃化转变中的重要作用。 如果发现具有不同动力学的空间域，则将通过实验确定它们的弛豫时间和内部结构。 这些潜在的变革性实验将是第一个直接的，结构性的探测器的存在，松弛和结构的空间异质动力学在纳米尺度。 该项目还将支持对75 at.%的金属玻璃的室温结构的研究。Ce和25原子% Al。这种玻璃具有一种新型的亚稳高压晶相，据推测，该晶相是由长程拓扑有序淬火成玻璃态而产生的。 传统的TEM将用于研究高压相的结构和缺陷，空间分辨纳米衍射将用于研究玻璃相的结构。该项目将支持STEM先进表征方法的教育和推广。 电子显微镜数据库，一个在线收集的例子数据集的教学和学习先进的STEM技术，将扩大，和底层的数据库技术将现代化。 参与本项目的研究人员将利用本项目所使用的STEM的远程操作功能，进行原子分辨率STEM成像和微观分析的公开讲座和演示。非技术概要玻璃是原子杂乱排列的材料，而晶体中的原子位于网格上。 大多数金属合金仅以晶体形式存在，但一些特殊的合金可以通过将其从液态熔化状态快速冷却而形成玻璃。 该项目将研究这些特殊的液体和它们形成的金属玻璃，以测量原子如何结合在一起，以及它们如何相对于彼此移动。 在这两种情况下，10-100个原子的团簇具有最重要的结构，其对应于约1纳米的尺寸。 该项目支持的研究人员将使用先进的电子显微镜进行测量，电子束直径为1纳米-刚好与有趣的原子团的大小相匹配。 他们的发现将帮助科学家理解为什么有些金属合金能形成玻璃，而有些不能，并可能导致开发出具有上级强度、延展性或其他性能的新金属玻璃。该项目还将支持美国新兴纳米技术劳动力所需的先进电子显微镜技术的教育和推广。 研究人员将维护和扩大电子显微镜数据库，一个在线收集的例子，用于教学和学习。 他们还将公开演示先进的电子显微镜，包括一次看到一个原子的能力，努力与年轻人分享他们对科学的兴趣和兴奋。

TECHNICAL SUMMARYThis project supports investigation of the structure and atomic dynamics of metallic glasses and metallic-glass forming liquids using systematic coherent electron nanodiffraction in a scanning transmission electron microscope, in a technique called fluctuation electron microscopy. Time-resolved nanodiffraction experiments as a function of temperature will test the hypothesis that metallic glass forming liquids exhibit spatial heterogeneous dynamics which play an essential role in their glass transition. If spatial domains with different dynamics are found, their relaxation time and their internal structure will be determined experimentally. These potentially transformative experiments will be the first direct, structural probe of the existence, relaxation, and structure of spatially heterogeneous dynamics at the nanometer scale. This project will also support investigation of the room-temperature structure of a metallic glass of 75 at.% Ce and 25 at.% Al. This glass has a novel metastable high-pressure crystalline phase, which has been proposed to arise from long-range topological order quenched into the glassy state. Conventional TEM will be used to investigate the structure and defects of the high-pressure phase, and spatially-resolved nanodiffraction will be used to investigate the structure of the glassy phase.The project will support education and outreach about advanced characterization methods in STEM. The Electron Microscopy Database, an online collection of example data sets for teaching and learning advanced STEM techniques, will be enlarged, and the underlying database technology will be modernized. The researchers involved in this project will conduct public lectures and demonstrations of atomic-resolution STEM imaging and microanalysis using the remote operation capabilities of the STEM used for this project's research.NON-TECHNICAL SUMMARYGlasses are materials in which the atoms are jumbled up, in contrast to crystals, in which the atoms sit on a grid. Most metal alloys exist only as crystals, but a few special ones can be forced to make a glass by cooling them very quickly from their liquid, melted state. This project will investigate those special liquids and the metallic glasses they form to measure how the atoms fit together and how they move around with respect to one another. In both cases, it is clumps of 10-100 atoms which have the most important structure, which corresponds to a size of about 1 nanometer. The researchers supported by this project will make their measurements using an advanced electron microscope with a beam of electrons one nanometer in diameter - just matched to the size of the interesting clumps of atoms. Their discoveries will help scientists understand why some metal alloys form glasses and others do not, and may lead to the development of new metallic glasses with superior strength, ductility, or other properties.This project will also support education and outreach in advanced electron microscopy techniques required for the nation's burgeoning nanotechnology workforce. The researchers will maintain and enlarge the Electron Microscopy Database, an online collection of examples for teaching and learning. They will also do public demonstrations of advanced electron microscopy, including the ability to see single atoms, one at a time, in an effort share with young people their interest and excitement about science.