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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