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Integrating Coherent Diffraction Imaging with Simulation
Integrating Coherent Diffraction Imaging with Simulation
Laser-heating-induced deformation of core-shell nanostructures
Scientific use case: Identifying fundamental deformation modes and comparing experiment (CDI) vs. simulation (FEM) for core-shell nanostructures heated with pulsed lasers.
Abstract: Visualizing the dynamical response of material heterointerfaces is increasingly important for the design of hybrid materials and structures with tailored properties for use in functional devices. In situ characterization of nanoscale heterointerfaces such as metal–semiconductor interfaces, which exhibit a complex interplay between lattice strain, electric potential, and heat transport at subnanosecond time scales, is particularly challenging. In this work, we use a laser pump/X-ray probe form of Bragg coherent diffraction imaging (BCDI) to visualize in three-dimension the deformation of the core of a model core/shell semiconductor–metal (ZnO/Ni) nanorod following laser heating of the shell. We observe a rich interplay of radial, axial, and shear deformation modes acting at different time scales that are induced by the strain from the Ni shell. We construct experimentally informed models by directly importing the reconstructed crystal from the ultrafast experiment into a thermo-electromechanical continuum finite element model (FEM). The model elucidates the origin of the deformation modes observed experimentally. Our integrated imaging approach represents an invaluable tool to probe strain dynamics across mixed interfaces under operando conditions.
Laser-heating-induced deformation of piezoelectric nanocrystals
Scientific use case: (Top) Finite element simulation of laser-induced-heating and subsequent deformation of piezoelectric ZnO nanocrystal. (Middle) Visualizing propagation of axial deformation mode during ultrafast pulsed laser heating of piezoelectric ZnO nanocrystal. (Bottom) Identifying fundamental deformation modes and comparing experiment vs. simulation.
Abstract: Imaging the dynamical response of materials following ultrafast excitation can reveal energy transduction mechanisms and their dissipation pathways, as well as material stability under conditions far from equilibrium. Such dynamical behavior is challenging to characterize, especially operando at nanoscopic spatiotemporal scales. In this letter, we use X-ray coherent diffractive imaging to show that ultrafast laser excitation of a ZnO nanocrystal induces a rich set of deformation dynamics including characteristic “hard” or inhomogeneous and “soft” or homogeneous modes at different time scales, corresponding respectively to the propagation of acoustic phonons and resonant oscillation of the crystal. By integrating the 3D nanocrystal structure obtained from the ultrafast X-ray measurements with a continuum thermo-electro-mechanical finite element model, we elucidate the deformation mechanisms following laser excitation, in particular, a torsional mode that generates a 50% greater electric potential gradient than that resulting from the flexural mode. Understanding of the time-dependence of these mechanisms on ultrafast scales has significant implications for development of new materials for nanoscale power generation.
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