Atomic-Scale Scanning Transmission Electron Microscopy and First-Principles Study of Functional Oxides
thesisposted on 27.11.2018 by Liang Hong
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Nanostructured transition-metal oxides have shown fascinating physical properties such as ferroelectricity, ferromagnetism and superconductivity. Most of these remarkable properties stem from the interplay between spin, lattice, charge, and orbital degrees at nanoscale surfaces, edges, defects and interfaces that are present in the nanostructures. In this Ph.D. dissertation, I investigate the atomic-scale structures and properties of several representative types of functional transition-metal oxide nanomaterials, including strontium titanate and barium titanate thin films, oxygen-functionalized MXene nanoribbons, lithium cobalt oxide nanoplatelets, and barium titanate nanocubes, using scanning transmission electron microscopy techniques and first-principles density functional theory simulations. The electronic properties of strontium titanate and barium titanate thin films with gallium arsenide are found to be correlated to the atomic arrangement and vacancies at the interfaces. The semiconducting property of MXene nanoribbons is demonstrated to be dependent on the size and edge shape of the nanoribbons. Lithium cobalt oxide nanoplatelets exhibit surface magnetism which are found to be tunable via introduction of aluminum. Ferroelectric orders in barium titanate nanocubes are found to be affected by surface and size effects. My research results reveal the importance of the structural confinement, atomic arrangement and bonding states between transition-metal and oxygen atoms to the physical properties of oxide materials. A fundamental understanding of the structure-property relationship in these oxide nanomaterials advances our ability to design and develop novel functional devices at nanoscale.