Structure, Dynamics, and Relaxation of Metallic Glasses at the Nanoscale

该项目支持对完全由金属原子组成的玻璃和液体的研究。在玻璃杯和液体中，原子都是无序排列的——像罐子里的弹珠一样乱糟糟地排列着，而不是像鸡蛋盒里的鸡蛋那样一排排地排列着。这种无序给测量原子如何排列以及它们如何相互运动的实验带来了特殊的问题。这个项目通过研究纳米直径的探针电子束如何与原子相互作用来解决这些问题，当电子束从一个地方移动到另一个地方，这揭示了它们是如何排列的，或者以固定的电子束位置作为时间的函数，这揭示了原子是如何移动的。了解原子的排列方式和运动方式将使研究人员能够理解玻璃材料物理学中的基本问题，包括：(1)液体是如何冷却成固体玻璃的？是液体的某些部分先停止运动，还是所有的原子同时减速？如果某些部分先停止，这些区域的原子排列有什么不同？(2)当给予玻璃中的原子一点热能时，它们是如何重新排列的？不足以融化，但足以移动一点？这个过程被称为老化，它可以使柔性金属玻璃变脆，但目前在原子尺度上对其知之甚少。这些问题的答案将为科学家们设计出具有高硬度、高成形性和高耐腐蚀性等理想性能的新型金属玻璃合金奠定科学基础。这些新材料可能会应用于从医疗设备和植入物到带有微小齿轮或其他滑动部件的纳米机器等领域。该项目将培训科学家和工程师创造新的金属玻璃材料，并了解它们如何在原子尺度上工作，它将通过使用电子显微镜的力量对单个原子（物质的基本组成部分）进行成像的现场演示，向K-12学生推广科学和工程。本项目将支持在纳米尺度上使用电子相关显微镜（ECM）和波动电镜（FEM）形式的相干电子纳米衍射研究金属玻璃和玻璃成型液体的非均质结构和动力学。过冷液体中的空间非均质动力学是许多玻璃化转变理论的核心，而玻璃中的时间非均质动力学是结构弛豫的核心。液体上的ECM实验将产生至少20年的动态长度尺度和液态动力学特征时间，并研究最近发现的近表层的玻璃化转变行为，其动力学速度至少比体快一个数量级。玻璃上的ECM实验将揭示产生结构弛豫的单个事件的大小和空间分布，FEM实验将深入了解弛豫前后玻璃的结构。新的ECM/FEM联合实验将使纳米结构和动力学之间的直接实验关联成为可能。在液体中，具有二十面体局部结构的区域具有较慢动力学的假设将得到验证，而在玻璃中，将开发工具和方法，以测量与单次弛豫事件相关的结构变化。总之，这些结果将检验现有的玻璃化转变和弛豫理论，并推动新理论的发展。通过简单键合获得的金属系统的见解具有跨材料类别的潜在影响，包括氧化物，硫族化物，小分子甚至聚合物玻璃。该项目产生的物理见解将为合理设计具有高玻璃成形能力和理想性能的金属玻璃合金奠定基础，这些性能包括高硬度，高弹性极限，高耐腐蚀性或生物良性腐蚀产品，适用于从生物医学设备和植入物到微或纳米机械的应用。该项目将通过持续更新电子显微镜数据库网站来支持教学和学习，并将通过向K-12学生展示使用高分辨率电子显微镜成像单个原子的现场演示来分享科学的兴奋。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARYThis project supports research into glasses and liquids consisting entirely of metal atoms. In both glasses and liquids, the atoms are arranged without order - jumbled up, like marbles in jar, not sitting in rows like eggs in an egg carton. That disorder poses special problems for experiments measuring how the atoms are arranged and how they move with respect to one another. This project addresses those problems by studying how nanometer-diameter probe beams of electrons interact with the atoms as the beam is moved from place to place, which reveals how they are arranged, or with a fixed beam position as a function of time, which reveals how the atoms move.Understanding how the atoms are arranged and how they move will enable researchers to understand fundamental questions in the materials physics of glasses, including: (1) How does a liquid cool into a solid glass? Do some parts of the liquid stop moving first, or do all the atoms slow down at once? If some parts stop first, what is different about the atomic arrangements in those regions? (2) How do the atoms in a glass rearrange when they are given just a little heat energy ? not enough to melt, but enough to move around a bit? This process is called aging, and it can make a flexible metallic glass brittle, but it is currently poorly understood at the atomic scale.Answers to these questions will lay the scientific groundwork for scientists to design new metallic glass alloys with desirable properties like very high hardness, high formability into parts, and high corrosion resistance. These new materials may find applications in areas ranging from medical devices and implants to nanomachines with tiny gears or other sliding parts. This project will train scientists and engineers to create new metallic glass materials and understand how they work at the atomic scale, and it will promote science and engineering to K-12 students through live demonstrations of imaging single atoms, the fundamental building blocks of matter, using the power of electron microscopy.TECHNICAL SUMMARYThis project will support investigation of the heterogeneous structure and dynamics of metallic glass and glass-forming liquids at the nanoscale using coherent electron nanodiffraction in the form of electron correlation microscopy (ECM) and fluctuation electron microscopy (FEM). Spatially heterogeneous dynamics in supercooled liquids are central to many theories of the glass transition, and temporally heterogeneous dynamics in the glass are central to structural relaxation.ECM experiments on liquids will yield a dynamic length scale and characteristic time for liquid-state dynamics over at least two decades in time, and investigate the glass transition behavior of a recently-discovered near-surface layer with dynamics at least one order of magnitude faster than the bulk. ECM experiments on glasses will reveal the size and spatial distribution of the individual events that create structural relaxation, and FEM experiments will yield insight into the structure of glasses before and after relaxation. New, combined ECM/FEM experiments will enable direct, experimental correlations between nanoscale structure and dynamics. In liquids, the hypothesis that regions with icosahedral local structure have slower dynamics will be tested, and in glasses, tools and approaches will be developed with the goal of measuring the changes in structure associated with single relaxation events. Together, these results will test existing theories of the glass transition and relaxation and drive development of new theories. The insights gained on metal systems with simple bonding have the potential for impact across materials classes, including oxide, chalcogenide, small molecule, and even polymer glasses.The physical insights generated by this project will lay the groundwork for rational design of metallic glass alloys with high glass forming ability and desirable properties including high hardness, high elastic limit, and either high corrosion resistance or biologically benign corrosion products for applications ranging from biomedical devices and implants to micro- or nanomechanical machines. This project will support teaching and learning through ongoing updating of the Electron Microscopy Database website, and it will share the excitement of science through live demonstrations to K-12 students of imaging single atoms using high-resolution electron microscopy.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.