Strength Design Maps for Nanoscale Metallic Multilayer Thin Films

技术：纳米多层薄膜是研究结构-力学性能关系的特殊系统。首先，这些体系表现出非凡的强度，远远超过具有类似晶粒度的单相体系的强度。其次，合成方法允许对组成和微观结构进行前所未有的控制，因此它们已成为研究结构、化学、界面和强度等物理性能之间关系的试验台。对于金属系统来说，这种强度取决于将滑动限制在较小体积的能力。目前，没有系统的方法来预测这种系统中的屈服强度，也不存在相应的系统验证方法。因此，多层薄膜领域缺乏广泛的设计策略来优化MEMS、硬涂层、折射光学元件、半导体带隙以及磁弹性和磁光薄膜等应用中的屈服强度。该计划的总体目标是开发和验证A/B金属多层膜的屈服强度设计图。这些图将包括作为输入的各个相性质、双分子层周期、体积分数、外延关系和外部负载的方向/符号。该方法是通过先进的基于位错的三维模拟技术、位错理论和新的实验验证方法的组合来改进现有的预测方法。这些措施包括通过X射线衍射测量验证内应力图；通过透射电子显微镜研究验证界面位错含量图；通过新型微柱测试和薄膜/基片弯曲测试验证屈服强度设计图。屈服强度设计图体现了对体积、面积和线能量如何驱动界面结构和内部应力状态的基本理解，以及这些特征如何将晶体滑移限制在较小的体积内。模拟结果和实验结果的比较将提供位错线能、内应力大小和界面势垒强度的值，这些值目前还不可用。将研究几个科学前提，包括屈服强度优化的具体策略。非技术：拟议的工作将推动纳米薄膜材料领域的发展。它还将加强教学、培训和学习的使命，促进代表不足群体的参与和专业发展。

Technical: Nanoscale multilayer thin films are extraordinary systems with which to study structure-mechanical property relations. First, these systems display remarkable strength, far surpassing the strength of single-phase systems with comparable grain size. Second, the methods of synthesis allow for unprecedented control of composition and microstructure, so that they have become a test bed to study correlations between structure, chemistry, interfaces, and physical properties such as strength. For metallic systems, that strength hinges on the ability to confine slip to small volumes. Currently, there exists no systematic means by which to predict yield strength in such systems, nor does a corresponding approach for systematic validation exist. Consequently, the multilayer thin film community lacks a broad design strategy to optimize yield strength in applications involving MEMS, hard coatings, refractive optical elements, band gaps for semiconductors, and magneto-elastic and magneto-optical films. The overall aim of the proposed program is to develop and validate yield strength design maps for A/B metallic multilayer thin films. These maps will include as input the individual phase properties, bilayer period, volume fractions, epitaxial relationships, and direction/sign of external loading. The approach is to advance current predictive methods through a combined program of advanced 3D dislocation-based simulation techniques, dislocation theory, and novel experimental verification methods. These include verification of internal stress maps via x-ray diffraction measurements; verification of interfacial dislocation content maps via transmission electron microscope studies; and verification of yield strength design maps via novel micropillar testing and film/substrate bend testing. Yield strength design maps embody a fundamental understanding of how bulk, area, and line energies drive interfacial structure and internal stress state and further, how these features confine crystallographic slip to small volumes. The comparison of modeling and experimental results will provide values of dislocation line energies, internal stress magnitudes, and interfacial barrier strengths that are not currently available. Several scientific premises will be examined, including specific strategies for yield strength optimization.Non-technical: The proposed work will advance the field of nanolayered thin-film materials. It will also strengthen the mission of teaching, training, and learning and promote the participation and professional development of underrepresented groups.