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

非技术性总结这个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--杂乱无章，就像罐子里的弹珠一样，而不是像鸡蛋盒里的鸡蛋一样排成一排。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电子探测光束在光束从一个地方移动到另一个地方时如何与原子相互作用来解决这些问题，这揭示了它们是如何排列的，或者是在固定的光束位置下是如何随时间变化的，这揭示了原子是如何运动的。理解原子是如何排列的以及它们是如何运动的将使研究人员能够理解玻璃材料物理中的基本问题，包括：(1)液体如何冷却成固体玻璃？是液体的某些部分先停止运动，还是所有的原子同时减速？如果有些部分先停止，那么这些区域的原子排列有什么不同？(2)玻璃中的原子在获得少量热能时如何重新排列？不足以融化，但足以四处走动？这个过程被称为时效，它可以使柔性金属玻璃变脆，但目前在原子尺度上对它的了解很少。回答这些问题将为科学家设计具有非常高的硬度、高成形性和高耐蚀性的新的金属玻璃合金奠定科学基础。这些新材料可能会在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得到应用。这个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进行成像的现场演示，向K-12年级的学生推广科学和工程学。技术总结本项目将支持在纳米尺度上使用电子相关显微镜(ECM)和波动电子显微镜(FE)形式的相干电子纳米衍射来研究金属玻璃和玻璃形成液体的非均质结构和动力学。过冷液体中的空间非均相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相动力学是结构松弛的核心。对液体的ECM实验将得到至少20年时间内液态动力学的动态长度尺度和特征时间，并研究最近发现的近表面层的玻璃转变行为，其动力学速度至少比块体快一个数量级。对玻璃的ECM实验将揭示产生结构松弛的单个事件的大小和空间分布，而有限元实验将深入了解玻璃松弛前后的结构。新的ECM/有限元联合实验将实现纳米级结构和动力学之间的直接实验关联。在液体中，将检验具有二十面体局部结构的区域具有较慢动力学的假设，在玻璃中，将开发工具和方法，目的是测量与单个弛豫事件相关的结构变化。总而言之，这些结果将检验现有的玻璃化转变和驰豫理论，并推动新理论的发展。通过简单键合的金属系统获得的见解可能会影响到各种材料类别，包括氧化物、硫化物、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形成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，应用范围从生物医疗设备和植入物到微型或纳米机械机械。该项目将通过不断更新电子显微镜数据库网站来支持教与学，并将通过现场演示向K-12年级的学生展示使用高分辨率电子显微镜对单原子进行成像的过程，分享科学的兴奋。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.