Investigation of High Strain-Rate Deformation and Failure of FCC and BCC Nanostructures

Overview: A research program is proposed, whose objective is to further understanding of the mechanical response of sub-150 nm-diameter FCC (Ag and Au) and BCC (Fe) metallic nanowires at high strain rate (up to 105 /s), comparing the effect of crystal structure (BCC Vs. FCC) and crystal topology (single crystal Vs. penta-twinned NWs), thus elucidating structure-property relationships of nanostructures at high strain rates. To accomplish this, experimental characterization of the nanowires will be performed employing previously-established techniques based on microelectromechanical systems (MEMS) mechanical characterization platforms, with capabilities of in-situ transmission electron microscopy (TEM) testing. For strain rates up to 103 /s, existing MEMS platforms can be readily used for the proposed characterization. Further improvements of the MEMS platforms, such as piezoelectric-based actuation and mass reduction are proposed to attain even higher strain rates, up to 105/s. Furthermore, for very high-strain rate experiments, coupling of MEMS testing and dynamic high speed TEM (DTEM) is planned, in order to obtain nanosecond-resolution imaging of the deformation processes occurring in the nanowires. Intellectual merit: The proposed synergy of state-of the-art experimental techniques, such as MEMS nanomechanical characterization, in-situ TEM, and DTEM, is expected to yield significant insights toward the understanding of high-strain rate mechanical behavior of metallic nanowires, dislocation processes in confined geometries of BCC and FCC metals, and validation of interatomic potentials for Molecular Dynamics (MD)-based modeling of metals. Given that nanostructures are envisioned to be applied in nanoelectronics or NEMS platforms, where frequencies of operation range from tens of kHz to GHz, high-strain rate mechanical testing will provide understanding of the behavior of nanostructures in dynamic applications. Furthermore, fundamental understanding of the mechanical properties of nanostructures, which is required to design and manufacture high performing, robust, and fail-tolerant nanoelectronic and NEMS devices, will be achieved. The proposed research will also bring experimental strain rates closer to those of MD simulations, which is critical to discover trends that validate the force fields used in MD. This validation will be extremely beneficial to atomistic modeling, not only for mechanical characterization, but for a breadth of scientific disciplines where MD simulations are used to gain insights on chemical, electrical and thermal material behavior. Broader Impacts: The educational and outreach component of this project will focus on providing opportunities to undergraduate and minorities students, through existing programs within the International Institute for Nanotechnology at Northwestern University, to participate in 9-week summer internships. Research experience for undergraduates (REU) and Minority internships on Nanotechnology (MIN) projects will focus on the experimental activities here proposed. Likewise, the PI will add a lab module on in-situ TEM testing of nanowires in the dual level course Experiments in Micro/Nano Science and Engineering he teaches at Northwestern University. A Youtube channel with videos of basic concepts of the proposed research will be started, in order to reach out to the general public.