1. UIC Physics Tessa Cooper Materials Science and Engineering Rutgers University Advisors: Dr. R. Klie and Q. Qiao Department of Physics, University of Illinois

2. UIC Physics  Project description.  Methods to be used.  Results obtained for bulk SrTiO 3.  Results obtained for SrTiO 3 /GaAs interface.

3. UIC Physics  Characterize ultra-thin SrTiO 3 film on GaAs using Transmission Electron Microscopy (TEM), Electron Energy Loss Spectroscopy (EELS), and multiple scattering calculations.  Determine the effects of having interfacial O vacancies and Ti diffusion in the substrate.  Evaluate potential uses of this material in electrical and other applications.

4. UIC Physics  Molecular Beam Epitaxy is used to deposit monolayer films of SrTiO 3 on GaAs. GaAs support SrTiO 3 (4 ML) Direct Deposition Sample 2 GaAs support Ti pre-layer (0.5 ML) SrTiO 3 (4 ML) Ti pre-layer Deposition Sample 1 Intensity (arb.units) (a) (b) (c) (d) 3940414243 44 Energy ( eV ) As 3d bare GaAs Ti/GaAs SrTiO 3 /GaAs (2) SrTiO 3 /GaAs (1) R.F. Klie, Y. Zhu, Applied Physics Letters, 87, 143106 (2005).

5. UIC Physics Highly distinct interfaces are formed, which do not display differences in atomic structure whether or not a prelayer is used. 2.0 nm GaAs SrTi O Schematic drawing of interface: R.F. Klie, Y. Zhu, Applied Physics Letters, 87, 143106 (2005). Z-contrast image, SrTiO 3

6. UIC Physics GaAs Semiconducting Highly resistive High electron mobility Direct band gap SrTiO 3 Dielectric constant of 300 Mature deposition method Good substrate for other oxides. GaAs on (110) plane SrTiO 3 on (100) plane 45°

7. UIC Physics The properties of this system make it ideal for transistors and other electronic applications. Prelayer Correct orientation Minimized defects GaAs SrTi O

8. UIC Physics Use image simulations and multiple scattering calculations to model the atomic and electric structures, which helps to…  Interpret experimental results.  Support theories that are not obvious through experimentation.

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10. UIC Physics  FEFF9 relies on Full Multiple Scattering calculations to produce x-ray or electron behavior in a material.  Other methods are Fourier based calculations, which require periodic structures.

11. UIC Physics  O electrons are ejected from the K shell, closest to the nucleus.  Ti electrons are ejected from L II or L III.

12. UIC Physics  Used FEFF9 to produce O K and Ti L edges in bulk SrTiO 3.  Constructed GaAs/SrTiO 3 interface to use with the multiple scattering calculations.  Used FEFF9 to produce O K and Ti L edges at the interface of SrTiO 3.  With Oxygen vacancies  Without vacancies

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15. UIC Physics Targeted a Ti atom at the middle of the interface from which to eject the electron, and removed O atoms around this atom. GaAsOTiSr

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17. UIC Physics Target a specific oxygen atom at the interface, and introduce oxygen vacancies surrounding that atom. GaAsOTiSr

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23. UIC Physics Targeted a specific oxygen atom at the center of the crystal structure, and introduced oxygen vacancies surrounding that atom. GaAsOTiSr

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25. UIC Physics  Bulk SrTiO 3 spectra can be reliably calculated for O K edge and Ti L edge.  Vacancy effect occurs in both Ti L edge and O K edge.  Oxygen vacancies can be shown by using FEFF9.

26. UIC Physics I would like to thank the following for making this research project possible: The National Science Foundation, EEC-NSF Grant # 1062943 and CMMI-NSF Grant # 1134753. Dr. Jursich and Dr. Takoudis The University of Illinois at Chicago