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

金属纳米线等纳米材料在从可伸缩电子学到纳米机电系统的许多设备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在设备应用中表征其可靠性、耐久性和生命周期性能至关重要。然而，由于实验和计算的缺陷，纳米线的可靠性还没有得到广泛的研究，纳米线的可靠性取决于多个时间尺度或应变率的形变和塑性，并且对于预测器件的使用寿命是必不可少的。该奖项支持关于金属纳米线的机械性能和可靠性如何由依赖于速率的塑性变形机制控制的基础研究。该奖项还支持：通过实际演示介绍研究，为中学生和高中生提供研究机会，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。这项研究将建立一个基本的理解，即应变率如何影响依赖于速率的塑性转变，从而在多个时间尺度上影响金属纳米线的机械行为和特性。利用一种新型的微电子机械系统器件进行了定量的原位电子显微镜实验，应变率范围为0.0001-100/S，通过应力-应变行为、激活参数的提取和缺陷动力学的原位电子显微镜观察来表征应变率对变形的影响。这一合作的一个关键特征是，实验将得到新的原子模拟的补充，这些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机械性能和观察到的变形机制的原子机制。具体地说，这些模拟将被用来捕捉扩散事件以及表面形核事件，以不仅阐明扩散对表面位错的贡献的机制，而且还阐明当扩散和位移变形同时起作用时出现的机制。最后，模拟将表征包含孪晶边界的纳米线的应变率相关的变形所产生的局域(脆性)或分布(延性)塑性。这一理解可能会改变关键技术，即可拉伸电子学、NEMS和光电子学，对于这些关键技术来说，金属纳米线是一个基本的构建块。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。

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.