Browsing by Author "Flannigan Lab, CEMS Department, University of Minnesota"

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    High-Resolution Analog of Time-Domain Phonon Spectroscopy in the TEM Experimental Data and Analysis 2019-2020
    (2020-03-16) VandenBussche, Elisah J; Flannigan, David J; flan0076@umn.edu; Flannigan, David J; Flannigan Lab, CEMS Department, University of Minnesota
    The behavior of coherent acoustic phonons (CAPs) as they propagate through a material is a function of the material’s optoelectronic and structural properties, making these collective oscillations a multi-faceted characterization tool. While CAPs are usually detected using transient reflectivity measurements, they have also previously been observed directly in real space using ultrafast electron microscopy (UEM). Here, we report use of UEM to measure localized CAP behavior in an amorphized and annealed GaAs specimen, and demonstrate the sensitivity of this measurement to atomic structure changes. The velocities are compared to expected values for speed of sound in order to draw conclusions about the degree of crystallinity of the specimen pre- and post-annealing. The ability to use a real-space technique to observe CAP behavior with high spatial resolution opens the door to measurements of spatially heterogeneous structural and optoelectronic properties. The data acquired in this experiment as well as analysis code are released here to enable open access to published data.
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    Supporting Data for Mitigating Damage to Hybrid Perovskites Using Pulsed-Beam TEM
    (2021-01-08) VandenBussche, Elisah J; Flannigan, David J; Holmes, Russell J; Clark, Catherine P; vand0837@umn.edu; VandenBussche, Elisah; Flannigan Lab, CEMS Department, University of Minnesota
    Using a pulsed-beam transmission electron microscope, we discover a reduction in damage to methylammonium lead iodide (MAPbI3) as compared to conventional beams delivered at the same dose rates. This work provides insights into damage processes and durability in hybrid perovskites and also illustrates the viability of using pulsed-beam TEM to explore the associated molecular-level routes to degradation, analogous to laser-accelerated energetic pulsed electron beams and the study of damage to biomolecules, cells, and tissues in radiobiology. The data acquired in this experiment are released here to enable open access to published data in accordance with MRSEC data policies.