Applied Physics Seminar: "Probing Atomic Structure Across Scale and Dimensions with Sub-Angstrom Electron Beams"

Modern materials are designed atomic layer by atomic layer with architectural complexity extending into the third dimension. Probing atomic structure across sub-Angstrom to micron scales in both two and three dimensions is therefore integral to the hierarchical engineering and design of future materials.
In 2D-materials—such as graphene, MoS2, and TaS2—reduced dimensionality leads to unique properties that could transform future of electronic devices. Local atomic structure of 2D materials dictates local topology which greatly influences electronic properties and implementation in actual devices. Using a modern electron microscope we can count the atoms across grain boundaries, identify stacking structure, and locate individual defects and dopants. Concurrently, diffraction techniques provide an understanding of structure across billions of atoms at larger length scales. In combination, we can obtain a complete description of the structure of 2D materials and correlate them with macroscopic properties. In multilayer graphene we use these methods to elucidate the rich structure of grain boundaries and stacking faults across length scales, a result which prompted the discovery that stacking order and twin boundaries dominate bulk transport behavior. In TaS2 we show the persistence and control of charge density waves (CDW) down to the ultrathin limit using cryogenic scanning transmission electron microscopy.
Three-dimensional characterization at the nano- and meso-scale in high resolution electron microscopes provides vital insights into a wide array of 3D nanomaterials, including hydrogen fuel cells, block-copolymer networks, and semiconductor devices. However achieving sub-nanometer resolution in three-dimensional reconstructions has not been possible due to a restriction known as the Crowther criterion, which forces a tradeoff between object size and resolution. Here we demonstrate a three-dimensional imaging method that overcomes this limit by combining through-focal depth sectioning and traditional tilt-series tomography to reconstruct extended objects, with sub-nanometer resolution, in all three dimensions.
In this talk, I will demonstrate how sub-Angstrom electron beams uncover structural insights spanning length scales of single atoms to billions of atoms in two and three dimensional materials.