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.

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North Carolina State University Raleigh
United States
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