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ion Structural Variability of La0.5Sr0.5TiO3 Thin Films

Yayoi Takamura, University of California-Davis, DMR 0747896Outcome: Researchers at UC Davis have demonstrated that exposure to an oxidizing environment can drive the spontaneous phase separation of a uniform La0.5Sr0.5TiO3 thin film into a ‘superlattice’ structure.Impact: The structure and electrical resistivity of La0.5Sr0.5TiO3 was shown to depend strongly on the exposure to reducing/oxidizing environments.Explanation: Transition metal elements such as Ti can exist in multiple valence states. For La0.5Sr0.5TiO3 , mixed Ti3+/Ti4+ valence is expected based on stoichiometry. However, under reducing conditions, oxygen vacancies result in a near Ti3+ valence state while under oxidizing conditions, the drive to reach the stable Ti4+ valence state leads to phase separation into regular and distorted perovskite regions as well as TiO2-rich stacking faults.

Scanning transmission electron microscopy images of uniform and phase separated

La0.7Sr0.3TiO3 films

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ion Strain Relaxation Defects: Stacking Faults and Nanoflowers

Yayoi Takamura, University of California-Davis, DMR 0747896

Outcome: Scanning and transmission electron microscopy was used to image the defect structures formed due to strain relaxation in perovskite oxide superlattices grown by pulsed laser deposition.Impact: A correlation was made between the growth conditions, defect structures and functional properties of perovskite oxide superlattices.Explanation: Artificial layered materials were synthesized by pulsed laser deposition, however, the lattice mismatch between layers leads to the formation of a variety of different defect structures. These structures are as subtle as stacking faults and as striking as the petals on a nanoflower.

Scanning and transmission electron microscopy images of stacking faults and nanoflowers found

in perovskite oxide superlattices

1m 0.1m

2 nm

Growth Direction

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The UC Davis Science, Technology, Engineering, Mathematics (STEM) Transfer Day brings prospective transfer students from community colleges with Mathematics Engineering Science Achievement (MESA) programs to UC Davis for a series of workshops and panels to learn about academic and research opportunities. 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.

STEM Transfer DayYayoi Takamura, University of California-Davis, DMR 0747896

Profs. Takamura and Jeoh during the Career Discovery Workshop, and students participating in hands on demonstrations by the Center for Biophotonics, Science and Technology (courtesy the Undergraduate Research Center, UC Davis)