Collaborative Research: Investigating the Strain-Rate and Time-Dependent Plasticity of Metal Nanowires

纳米材料，如金属纳米线，在从可拉伸电子到纳米机电系统的许多器件应用中发挥着关键作用。了解其随时间变化的变形和失效机制对于表征其在设备应用中的可靠性、耐久性和生命周期性能至关重要。然而，由于实验和计算上的缺陷，纳米线的可靠性尚未得到广泛的研究。纳米线的可靠性取决于在多个时间尺度或应变速率下的变形和塑性，这对预测器件在其寿命期间的性能至关重要。该奖项支持关于如何通过速率相关的塑性变形机制控制金属纳米线的机械性能和可靠性的基础研究。该奖项还支持：通过实际演示推广研究，为初中和高中学生提供研究机会，以及加强波士顿大学和北卡罗来纳州立大学的本科力学课程。本研究将对应变速率如何影响速率相关的塑性转变以及金属纳米线在多个时间尺度上的力学行为和性能建立一个基本的理解。采用应变速率为0.0001 ~ 100 /s的新型MEMS器件进行原位定量TEM实验。应变速率对变形的影响将通过应力-应变行为、激活参数的提取和缺陷动态的原位透射电镜观察来表征。这次合作的一个关键特征是，实验将由新的原子模拟来补充，这种模拟可以访问将在实验中应用的时间尺度和应变率，这将阐明支撑实验测量的力学性能和观察到的变形机制的原子机制。具体来说，模拟将用于捕获扩散事件和表面成核事件，不仅阐明扩散导致表面位错的机制，而且还阐明扩散和位移变形同时发生时出现的机制。最后，模拟将表征局部（脆性）或分布（延性）塑性，这些塑性是由含孪晶界的纳米线的应变率相关变形产生的。这种理解可能会改变关键技术，即可拉伸电子学、NEMS和光电子学，金属纳米线是这些技术的基本组成部分。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。

Nanomaterials such as metal nanowires play a critical role in many device applications ranging from stretchable electronics to nanoelectromechanical systems. Understanding their time-dependent deformation and failure mechanisms is essential for characterizing their reliability, durability and life-cycle performance in device applications. However, due to both experimental and computational shortcomings, the reliability of nanowires, which depends on deformation and plasticity over multiple time scales or strain rates, and which is essential to predicting device performance over its lifespan, has not been widely investigated. This award supports fundamental research on how the mechanical properties and reliability of metal nanowires are controlled by rate-dependent plastic deformation mechanisms. This award also supports: outreach to introduce research through practical demonstrations and to provide research opportunities for middle school and high school students, and the enhancement of undergraduate mechanics courses at both Boston University and North Carolina State University.This research will establish a fundamental understanding of how strain rate impacts the rate-dependent plasticity transitions, and thus the mechanical behavior and properties of metal nanowires across multiple time scales. Quantitative in-situ TEM experiments will be carried out using a novel MEMS device with the strain rate ranging from 0.0001 to 100 /s. Strain rate effects on deformation will be characterized through stress-strain behavior, extraction of activation parameters, and in-situ TEM observation of defect dynamics. A key feature of this collaboration is that the experiments will be complemented by novel atomistic simulations that can access the time scales and strain rates that will be applied experimentally, which will elucidate the atomistic mechanisms underpinning the experimentally- measured mechanical properties and observed deformation mechanisms. Specifically, the simulations will be used to capture both diffusional events, as well as surface nucleation events to not only elucidate the mechanisms by which diffusion contributes to surface dislocation, but also the mechanisms that emerge when diffusive and displacive deformations are simultaneously operant. Finally, the simulations will characterize the localized (brittle) or distributive (ductile) plasticity that emerges from strain-rate-dependent deformation of nanowires containing twin boundaries. This understanding may transform the key technologies, i.e., stretchable electronics, NEMS, and optoelectronics, for which metal nanowires represent a fundamental building block.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.