Presented by Peng Zuo at International Conference on Crystal Growth and Epitaxy (ICCGE-19) in Keystone CO, July 28-August 2, 2019. Solid phase epitaxy (SPE) is a promising approach for expanding the applications of epitaxial complex oxides by providing access to a broader range of compositions and enabling their formation in complex geometries. The SPE of PrAlO3 on SrTiO3 serves as a model system. The interfaces between lanthanide aluminates and SrTiO3 are also of practical interest because these interfaces can host a two-dimensional electron gas. Amorphous PrAlO3 layers were deposited on the SrTiO3 (001) by atomic layer deposition using tris(isopropylcyclopentadienyl)praseodymium (Pr(C5H4iPr)3), trimethylaluminum (AlMe3) and water.

1. Solid Phase Epitaxy of PrAlO3 on SrTiO3:
A New Growth Approach for Complex
Oxide Thin Films and Interfaces
Peng Zuo,1 Yajin Chen,1 Wathsala L. I. Waduge,2 Navoda Jayakodiarachchi,2 Deepankar
Sri Gyan,1 Donald Savage,1 Thomas F. Kuech,3 Charles H. Winter,2 Susan E. Babcock1
and Paul G. Evans1
1. Department of Materials Science and Engineering, University of Wisconsin-Madison
2. Department of Chemistry, Wayne State University
3. Department of Chemical and Biological Engineering, University of Wisconsin-Madison
1

2. To Create 3D PrAlO3/SrTiO3 Interfaces
2
• PrAlO3/SrTiO3:
• 2-Dimensional Electron Gas (2DEG)
• Pulsed Laser Deposition: limited to
planar geometries
A. Annadi et al. PRB, 86(2012), 085450.
New Growth Method Needed for More Complex 3D Geometries
• Atomic Layer Deposition (ALD):
• Allows 3D Geometries: good conformality
• Current Limitations: precursors not self-limited

3. Structure Similarity of PrAlO3 & SrTiO3
3
PrAlO3:
Rhombohedral, a= 5.307 Å, 𝞪=60.33∘
Pseudocubic (FCC), a/2 ~ 3.753 Å
Al
O
Pr
SrTiO3:
Cubic, a= 3.905 Å Sr
Ti
O
Same Octahedra Packing

4. Key Issues
4
• New ALD Process for PrAlO3
• Crystallization Process:
• Epitaxial 𝞬-Al2O3 Layer at the PrAlO3/SrTiO3 Interface As-deposited
• Highly (001)-Oriented PrAlO3 Films after Thermal Annealing

5. Experimental Process
5
• Amorphous PrAlO3 Grown by Atomic Layer Deposition (ALD)
In collaboration with Prof. Charles Winter Group from Wayne State University
• New Precursors: Pr(C5H4iPr)3, AlMe3, Water
• Deposition @ 300∘C, Films Thickness ~206 nm
• Thermal Annealing in A Range of Temperatures between 500 ∘C and
1000 ∘C, and Durations between 20 min and 11 h

6. Average Amorphous PrAlO3 Films As-Deposited
6
W. L. I. Waduge et al., submitted 2019.
Grazing-Incidence X-ray Diffraction

7. EDS
Al-Rich Layer at Interface As-Deposited
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STEM-HAADF
50 nm
PrAlO3
SrTiO3
Dark Interfacial Layer ~4 nm
PrAlO3
SrTiO3
20 nm
Al-rich Interfacial Layer ~4 nm
STEM-HAADF
Average Composition
[Pr] : [Al] = 1 : 1.25
Wavelength Dispersive
Spectroscopy – Electron Probe
MicroAnalysis

8. 8
Epitaxial 𝞬-Al2O3 at Interface As-Deposited
STEM-HAADF
Interfacial
Layer
SrTiO3
~1.95 Å
~1.94 Å
Sr
Ti, O 1 nm
[001]
[100]
𝞬-Al2O3: cubic, a=7.900 Å
1.975 Å
Al
O

9. 9
X-ray 𝛉-2𝛉 Scan Along SrTiO3 Qz Direction
• The Sample Annealed at 800∘C, 3h
W. L. I. Waduge et al., submitted 2019.
FCC 002
FCC 004
X-ray Phi Scan
Epitaxial PrAlO3 Films Grown on the 𝞬-Al2O3 Layer

10. Epitaxial PrAlO3 Films Grown on the 𝞬-Al2O3 Layer
10
1 nm
STEM-HAADF• 800∘C, 1h
PrAlO3
𝞬-Al2O3
SrTiO3
[100]
[001]
[100]
[001]

11. Model for Epitaxial PrAlO3 Films on 𝞬-Al2O3
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Al
O
𝞬-Al2O3 (001) faceFCC-PrAlO3 (001) face
~ 5% Mismatch

12. Conclusions & Perspectives
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We gratefully acknowledge funding from the
National Science Foundation, DMR-1720415
• Supervisors: Prof. Susan E. Babcock, Prof. Paul G. Evans, Prof. Thomas F. Kuech
• Collaborators: UW-Madison: Yajin Chen, Deepankar Sri Gyan, Dr. Donald Savage; Wayne
State University: Prof. Charles H. Winter, Dr. Wathsala L. I. Waduge, Navoda
Jayakodiarachchi
Acknowledgement
• New ALD Growth Method Developed for PrAlO3
• Epitaxial 𝞬-Al2O3 Layer Grown on (001) SrTiO3 As-deposited
• To Explore the Role of the 𝞬-Al2O3 Layer in PrAlO3 Solid Phase Epitaxy
• Developing Alternative Precursors for Pr

13. 13
Thank You for Your Attention!