Physics Colloquium

Dr. Albina Y. Borisevich, Oak Ridge National Laboratory

"Surface and Interface Phenomena in Oxides by Quantitative Scanning Transmission Electron Miocroscopy"

4:15pm, The John A. Wheeler Lecture Hall (RLM 4.102). Coffee and cookies will be served at 4:00pm in RLM 4.102

Abstract: Oxide materials offer promise of multiple functionalities that can be tailored via interface engineering or chemical substitution. Their magnetic, electrical, and structural properties are tied to the subtle distortions of the crystallographic lattice from the perfect prototype. Atomic-scale understanding of all aspects of materials behavior: strain, polarization, charge transfer is necessary to understand and predict novel properties. Aberration corrected scanning transmission electron microscopy (STEM) can provide direct structural and chemical information at the unit cell level. For materials with several competing functionalities, the properties can be affected both by structural order parameters and chemical factors, such as cation segregation, compositional gradients, or oxygen vacancy formation. These effects are especially significant in the vicinity of surfaces and heterointerfaces.

Interpreting experimental data in the framework of Landau-Ginsburg-Devonshire and /or Density Functional theory enables us to build a complete picture of the material behavior. Tracking different order parameters in the vicinity of the BiFeO3 surface, we can resolve discrepancies in the estimates of the ferroelectric “dead layer” thickness obtained by different techniques. We were also able to study the local electronic and magnetic structure variations in the bulk and at the surfaces of digital superlattices (LaFeO3)n(SrFeO3) for n = 2, 8, uncovering variations in crystal field splitting and oxygen coordination and connecting them to the local geometries of the metal-oxygen bonds. Finally, we can demonstrate that STEM data can be used to reveal three-dimensional information about octahedral tilts in the system. Incorporation of advanced data processing techniques into analysis of structural and spectroscopic data will also be discussed.

Acknowledgements: This research was supported by the Materials Sciences and Engineering Division, Office of Basic Energy Sciences (BES), U.S. Department of Energy (DOE), and via user proposals to ORNL’s Center for Nanophase Materials Sciences, which is supported by the Scientific User Facilities Division, DOE BES. This research used resources of the National Energy Research Scientific Computing Center.