1. Center for Functional Nanomaterials Seminar

    "Resolving Atomic and Electronic Structure Ordering in Emerging Materials using Advanced STEM"

    Presented by Ye Zhu, The Hong Kong Polytechnic University, Hong Kong

    Thursday, September 3, 2020, 8:30 am
    https://teams.microsoft.com/l/meetup-join/19%3amee

    Hosted by: Dr. Charles Black

    Novel functional materials are usually characterized by emerging ordering in atomic and electronic structures beyond the conventional unit-cell level. Examples include artificial superlattices, self-assembled nanostructures, ferroic domain structures, and charge-density waves. Such complex ordering gives rise to large supercells containing too many atoms, making it a formidable task for diffraction-based structure determination. On the other hand, the maturation of aberration-corrected TEM/STEM presents an alternative real-space approach to probe the complex ordering, through directly imaging the atomic structure with picometer precision, as well as the spatially-resolved spectroscopy to map the electronic structure. Here I will give several examples showing the power of advanced STEM on resolving the complex ordering: i) By developing an imaging condition optimized for oxygen contrast, we can image sensitively the octahedral structure in perovskite oxides with picometer precision. It further enabled us to reveal an extraordinary 2D ordered octahedral tilting in the solid electrolyte Li0.5-3xNd0.5+xTiO3, and to demonstrate its dependence on the competition between Li% and lattice strain.[1] ii) Through atomic displacement mapping using high-resolution imaging, and electric polarization mapping based on 4D-STEM, we made the first experimental discovery of 2D antiferroelectricity in In2Se3, and resolved the true nature of its superstructure that had been under debate for over four decades.[2] iii) In the last example, we applied atomic-scale electron energy-loss spectroscopy to unravel the distinct configurations and valence states of Ce dopants in Mn3O4 nanocatalysts, which suggested an effective oxygen-storage/release route that is responsible for the enhanced redox catalytic activity from Ce doping.[3] [1] Nature Materials 14, 1142-1149 (2015). [2] Physical Review Letter 125, 047601 (2020). [3] Chemistry of Material 31, 5769-5777 (2019).