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

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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.