Methods in Characterizing the GaAs-SrTiO 3 Interface
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Transcript of Methods in Characterizing the GaAs-SrTiO 3 Interface
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Tessa CooperMaterials Science and EngineeringRutgers University
Advisors: Dr. R. Klie and Q. QiaoDepartment of Physics, University of Illinois
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Project description.
Methods to be used.
Results obtained for bulk SrTiO3.
Results obtained for SrTiO3/GaAs interface.
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Characterize ultra-thin SrTiO3 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.
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Molecular Beam Epitaxy is used to deposit monolayer films of SrTiO3 on GaAs.
GaAs support
SrTiO3 (4 ML)
Direct Deposition
Sample 2
GaAs support
Ti pre-layer (0.5 ML)
SrTiO3 (4 ML)
Ti pre-layer Deposition
Sample 1
Inte
nsity
(arb
.uni
ts)
(a)
(b)
(c)
(d)
39 40 41 42 43 44 Energy ( eV )
As 3d
bare GaAs
Ti/GaAs
SrTiO3/GaAs (2)
SrTiO3/GaAs (1)
R.F. Klie, Y. Zhu, Applied Physics Letters, 87, 143106 (2005).
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Highly distinct interfaces are formed, which do not display differences in atomic structure whether or not a prelayer is used.
2.0 nm Ga As Sr Ti O
Schematic drawing of interface:
R.F. Klie, Y. Zhu, Applied Physics Letters, 87, 143106 (2005).
Z-contrast image, SrTiO3 Z-contrast image, SrTiO3
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GaAs•Semiconducting •Highly resistive•High electron mobility•Direct band gap
SrTiO3•Dielectric constant of 300 •Mature deposition method •Good substrate for other oxides.
GaAs on (110) plane SrTiO3 on (100) plane
45°
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The properties of this system make it ideal for transistors and other electronic applications.
Prelayer Correct orientation Minimized defects
Ga As Sr Ti O
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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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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.
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O electrons are ejected from the K shell, closest to the nucleus.
Ti electrons are ejected from LII or LIII.
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Used FEFF9 to produce O K and Ti L edges in bulk SrTiO3.
Constructed GaAs/SrTiO3 interface to use with the multiple scattering calculations.
Used FEFF9 to produce O K and Ti L edges at the interface of SrTiO3. With Oxygen vacanciesWithout vacancies
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Targeted a Ti atom at the middle of the interface from which to eject the electron, and removed O atoms around this atom.
Ga As OTi
Sr
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Target a specific oxygen atom at the interface, and introduce oxygen vacancies surrounding that atom.
Ga As OTi
Sr
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Targeted a specific oxygen atom at the center of the crystal structure, and introduced oxygen vacancies surrounding that atom.
Ga As OTi
Sr
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Bulk SrTiO3 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.
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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