4D STEM experiments enabled by high-speed direction electron detectors

Traditional scanning transmission electron microscopy (STEM) detectors are large, single pixels that integrate a subset of the transmitted electron beam signal scattered from each electron probe position. These transmitted signals are extremely rich in information, containing localized information on sample structure, composition, phonon spectra, 3D defect crystallography, and more. Conventional STEM imaging experiments record only 1 – 2 values per probe position, throwing away most of the diffracted signal information. With the introduction of extremely high-speed direct electron detectors, we can now record a full image of the diffracted electron probe at each position, producing a four-dimensional dataset we refer to as a 4D STEM experiment. In this talk, the challenges and opportunities created by 4D STEM are discussed. The experiments that were covered: Mapping out local structure and composition by matching the experimental patterns to diffraction simulations; local strain measurements over a very large field of view using nanobeam electron diffraction; virtual dark-field imaging using arbitrary detectors; and phase contrast imaging methods in STEM, such as ptychography, MIDI-STEM, and multibeam STEM holography. Presenter: Colin Ophus, Molecular Foundry, Berkeley Lab