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Characterizing local structure in complex oxides with quantitative scanning transmission electron microscopy

  • Author(s): Zhang, Jack Y.
  • Advisor(s): Stemmer, Susanne
  • et al.
Abstract

Perovskite oxides remain a material class with properties that can be difficult to predict. Strong electron correlations, coupling between electron, lattice, spin and orbital degrees of freedoms, combined with the versatility of the structure itself, result in a wide range of properties, with unique emergent phenomena that occur only at heterointerfaces. Structure plays an especially important role in determining the properties of perovskite oxides. Small distortions in the lattice, particularly rotations or tilts of the oxygen octahedra, can have large effects on the material’s electrical and magnetic properties. One way we can tune these rotations is by growing thin film heterostructures, allowing us to tailor the properties of these materials in ways not possible in the bulk. Therefore, determining the local atomic structure in these films is critical for understanding the structure-property relationships, and the origin of any emergent behavior that may exist at an interface.

To that end, we utilize scanning transmission electron microscopy (STEM) to develop a link between the atomic structure and electrical/magnetic properties of three different systems: SrTiO3 quantum wells between GdTiO3 and SmTiO3, GdTiO3 quantum wells between SrTiO3, and strained NdNiO3. Using real-space and diffraction techniques, we obtain quantitative information on local octahedral rotations and observe the presence/absence of structural transitions. This information gives us new insight into the

driving forces behind the metal-insulator transition and magnetic behavior of the different material systems. We also continue the development of quantitative STEM for precise and accurate determination of 3D dopant atom configurations by using variable detector angles in the high angle annular dark field regime. By demonstrating the usefulness of obtaining angle-resolved scattering data, we provide a new avenue for improving STEM image contrast and atom visibility for future studies.

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