Credit: Reprinted with permission from Applied Physics Letters. Copyright 2016, AIP Publishing LLC. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the AIP Publishing LLC.
High-energy electrons coupled to a laser were used to probe the atomic motion induced in a thin film of gold. A 2-dimensional detector measured the intensity and direction of the electrons scattered from the gold atoms. The measured change in the electron scattering with and without exposure to the laser beam (the laser excites the atoms, increasing their vibrations) is shown in the top image. The scattering is strongest in the regular array of dark blue spots in the image associated with the average position of the atoms in their crystalline array. The hazy region, or speckle, around a strong saturated peak (bottom right) is compared to a calculation (bottom left) of the directionally dependent diffuse scattering related to collective thermal motion of atoms. Such measurements are important for understanding energetic states and thermal transport in materials -- foundational for many technologies, such as thermoelectric devices