Methods in characterizing the gaas srtio 3 interface
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Tessa Cooper Materials Science and Engineering Rutgers University Advisors: Dr. R. Klie and Q. Qiao Department of Physics, University of Illinois. Methods in Characterizing the GaAs-SrTiO 3 Interface. Overview. Project description. Methods to be used.

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Methods in Characterizing the GaAs-SrTiO 3 Interface

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Tessa Cooper

Materials Science and Engineering

Rutgers University

Advisors:

Dr. R. Klie and Q. Qiao

Department of Physics, University of Illinois

Methods in Characterizing the GaAs-SrTiO3 Interface


Overview

  • Project description.

  • Methods to be used.

  • Results obtained for bulk SrTiO3.

  • Results obtained for SrTiO3/GaAs interface.


Overview of the project

  • 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.


SrTiO3/GaAs (1)

As 3d

(d)

SrTiO3 (4 ML)

SrTiO3 (4 ML)

SrTiO3/GaAs (2)

(c)

Ti pre-layer (0.5 ML)

Intensity (arb.units)

GaAs support

GaAs support

Ti/GaAs

(b)

bare GaAs

(a)

3940414243 44

Energy (

eV

)

How are these films made?

  • Molecular Beam Epitaxy is used to deposit monolayer films of SrTiO3 on GaAs.

Sample 2

Sample 1

Ti pre-layer Deposition

Direct Deposition

R.F. Klie, Y. Zhu, Applied Physics Letters, 87, 143106 (2005).


Schematic drawing of interface:

O

Ga

As

Sr

Ti

2.0 nm

What do the films look like?

Highly distinct interfaces are formed, which do not display differences in atomic structure whether or not a prelayer is used.

Z-contrast image, SrTiO3

Z-contrast image, SrTiO3

R.F. Klie, Y. Zhu, Applied Physics Letters, 87, 143106 (2005).


Are the materials important?

GaAs

  • Semiconducting

  • Highly resistive

  • High electron mobility

  • Direct band gap

SrTiO3

  • Dielectric constant of 300

  • Mature deposition method

  • Good substrate for other oxides.

45°

GaAs on (110) plane SrTiO3 on (100) plane


How can this system be used?

The properties of this system make it ideal for transistors and other electronic applications.

O

Ga

As

Sr

Ti

  • Prelayer

  • Correct orientation

  • Minimized defects


What are my project goals?

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.


What does FEFF require?


How do the simulations work?

  • 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.


What do the edges mean?

  • O electrons are ejected from the K shell, closest to the nucleus.

  • Ti electrons are ejected from LII or LIII.


What have I accomplished?

  • 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 vacancies

    • Without vacancies


Comparison with FEFF9 results


Comparison with FEFF9 results


Construction of Interface

As

Ti

Sr

O

Ga

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


Simulated results (Ti L edge)


Construction of Interface

As

Ti

Sr

O

Ga

Target a specific oxygen atom at the interface, and introduce oxygen vacancies surrounding that atom.


Simulated results (O K edge)


Simulated results (O K edge)


Simulated results (O K edge)


Simulated results (O K edge)


Simulated results (O K edge)


Construction of Interface

As

Ti

Sr

O

Ga

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


Simulated results (O K edge)


Summary

  • 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.


Acknowledgments

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


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