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ion Non-Destructive Structural Characterization Technique

Yayoi Takamura, University of California-Davis, DMR 0747896

Thomson scattering factor and the real part of the dispersion correction factor (f0+f’) as a function of energy, XRR spectra at different energies for two superlattices (courtesy of Y. Takamura)

Outcome: Researchers at UC Davis, Stanford Synchrotron Radiation Lightsource and the Center for Nanophase Materials Sciences have demonstrated the structural characterization of perovskite oxide superlattices using resonant x-ray reflectivity (XRR). Impact: This non-destructive technique provides detailed structural parameters (layer thickness, roughness, density) which otherwise would require transmission electron microscopy techniques.Explanation: Absorption of x-rays by a material (measured by f0+f’) changes dramatically at the absorption edges of the constituent elements due to electronic transitions in the atoms. By tuning the x-ray energy to the absorption edges (red/blue curves), resonant XRR permits the distinction between layers with similar density. An example of two [6La0.7Sr0.3FeO3] [3La0.7Sr0.3MnO3]10 superlattices with sharp (A) and graded (b) interfaces is shown. A conventional spectra measured at 8000 eV is shown in green.

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ion Functional Properties of Materials Interfaces

Yayoi Takamura, University of California-Davis, DMR 0747896

Explanation: Perovskite oxide superlattices where the layer thicknesses are controlled down to unit cell thicknesses are shown to possess properties that differ from their bulk counterparts or single layers. Electronic reconstruction involving the movement of electrons across interfaces was shown to have a profound effect on the ferromagnetic (FM) properties of LSMO layers. When paired with La0.5Sr0.5TiO3 (LSTO) layers, robust FM properties are observed down to 6 unit cell thicknesses.

Prof. Takamura and a student observing the pulsed laser deposition system. (courtesy of UC Davis College of Engineering)

Outcome: Researchers at UC Davis, Lawrence Berkeley National Laboratory and the Center for Nanophase Materials Sciences have investigated the functional properties of the interfaces of perovskite oxide superlattices grown by pulsed laser deposition. Impact: The functional properties of La0.7Sr0.3MnO3

(LSMO) layers were shown to depend on the layer thickness and the identity of the second layer in the superlattice.

Z-contrast image of LSMO/LSTO superlattices. (courtesy of Y. Takamura)

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ion STEM Transfer Day

Yayoi Takamura, University of California-Davis, DMR 0747896Takamura is a major sponsor of the UC Davis Science, Technology, Engineering, Mathematics (STEM) Transfer Day. This one-day event brings together prospective transfer students from community colleges with Mathematics Engineering Science Achievement (MESA) programs from around California for a series of workshops and panels to learn about the academic and research opportunities available at UC Davis. The MESA programs are designed to aid educationally disadvantaged students to prepare for and graduate from a four-year college. These programs have a proportionally higher percentage of students who are under-represented minorities, women, and first generation college attendees. About 20% of past attendees have enrolled at UC Davis, where they have excelled academically. Students participating in the Information Fair and hands

on demonstrations (courtesy the Undergraduate Research Center, UC Davis)