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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Methods in characterizing the gaas srtio 3 interface

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

Overview

  • Project description.

  • Methods to be used.

  • Results obtained for bulk SrTiO3.

  • Results obtained for SrTiO3/GaAs interface.


Overview of the project

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.


How are these films made

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).


What do the films look like

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

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

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

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

What does FEFF require?


How do the simulations work

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

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

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


Comparison with feff9 results1

Comparison with FEFF9 results


Construction of interface

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

Simulated results (Ti L edge)


Construction of interface1

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 edge1

Simulated results (O K edge)


Simulated results o k edge2

Simulated results (O K edge)


Simulated results o k edge3

Simulated results (O K edge)


Simulated results o k edge4

Simulated results (O K edge)


Construction of interface2

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 edge5

Simulated results (O K edge)


Summary

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

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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