High-Resolution Analog of Time-Domain Phonon Spectroscopy in the TEM Experimental Data and Analysis 2019-2020

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.