Yajin Chen presented her work on the use of solid-phase epitaxy to create epitaxial complex-oxide interfaces that have promising electronic properties at the APS March Meeting 2019 in Boston, MA. The presented work is a part of a collaborative project with Prof. Charles H. Winter’s group in the Department of Chemistry at Wayne State University. Epitaxial RAlO3/SrTiO3 (R = La, Pr, Nd) oxide interfaces can produce a two-dimensional electron gas (2DEG), but the creation of those interfaces is limited to 2D geometries. Intricate geometries of epitaxial oxide thin films can be created by crystallizing the amorphous layers with thermal heating, which is termed solid-phase epitaxy. Atomic layer deposition (ALD) is employed to deposit the amorphous layers because ALD allows for the conformal deposition of thin films over non-planar surfaces. Prof. Winter’s group successfully developed the growth of amorphous PrAlO3 thin films by ALD. Epitaxial PrAlO3 thin films were achieved on single-crystal (001) SrTiO3 substrates with solid-phase epitaxy through the development of new ALD procedures, by understanding of the crystallization kinetics, and by probing the microstructure and interface structures of the crystallized thin films.

1. University of Wisconsin-Madison Department of Materials Science and Engineering
Solid-Phase Epitaxy of Atomic
Layer Deposited PrAlO3 Films
Yajin Chen,1 Wathsala L. I. Waduge,2 Peng Zuo,1 Thomas F. Kuech,3 Susan
E. Babcock,1 Charles H. Winter2 and Paul G. Evans1
ychen446@wisc.edu
1Department of Materials Science and Engineering, University of Wisconsin-
Madison, Madison, WI 53706, USA
2Department of Chemistry, Wayne State University, Detroit, MI 48202, USA
3Department of Chemical and Biological Engineering, University of
Wisconsin-Madison, Madison, WI 53706, USA

2.  Polar/nonpolar oxide interfaces REBO3/SrTiO3 (100) (RE = La, Pr, or Nd, B =
Al or Ga) all produce two-dimensional electron gases (2DEG).
 Vapor-phase epitaxial growth techniques are limited in two-dimensional
geometries.
Limitation in the creation of complex oxide quantum
electronic heterostructures
2
A. Annadi et al., Phys. Rev. B 86, 085450 (2012)

3.  Solid phase epitaxy (SPE)
• Low deposition temperature  A wider range of compositions
• Patterned substrates  Deposition in 3D geometries
 SPE may allow the creation of 2DEG at complex oxide interfaces in new
geometries.
Novel method to expand compositions and geometries
3Y. Chen et al., ACS Appl. Mater. Interfaces 9, 41034-41042 (2017)
Y. Chen et al., J. Phys. Chem. C (2019)
Amorphous
Single Crystal
Substrate
Mask
P. G. Evans et al., Curr. Opin. Solid State
Mater. Sci. 22, 229 (2018)

4. Slow crystallization of amorphous PrAlO3 on SiO2/Si
4
 43-nm-thick PrAlO3 film on a
SiO2/Si substrate grown by
atomic layer deposition at
300 °C.
 Grazing-incidence x-ray
scattering indicates the film
is amorphous.
 The film remains
amorphous after annealing
at 1000 °C for 8 h.
W. Waduge et al., Solid Phase Epitaxy of PrAlO3 Films
Grown by Atomic Layer Deposition, In preparation (2019)

5. Crystallization of amorphous PrAlO3 on (001) STO
5
 206-nm-thick PrAlO3 film on
a TiO2-terminated SrTiO3
(STO) (001) substrate
grown by atomic layer
deposition at 300 °C.
 The amorphous film fully
crystallizes after annealing
at a relatively lower
temperature, 800 °C for 3h.

6. 6
 Only crystalline PrAlO3 phase forms.
 Crystallized PrAlO3 film shows texture along [001] orientation.
Only crystalline PrAlO3 phase forms
 PrAlO3 pseudo-cubic structure with a = 3.772 Å[1]
SrTiO3 cubic structure with a = 3.905 Å
[1] K. Yang et al. Scientific reports 6, 34667 (2016)

7. Characterization of [001]-oriented PrAlO3 film
7
θ-2θ scan along sample normal Rocking curve measurement
 Crystallized PrAlO3 film is highly
[001]-oriented, the same
orientation as the STO substrate.
 FWHM = 7°

8. Conclusion & Acknowledgements
8
 Develop ALD procedures to deposit amorphous PrAlO3 thin films.
 Achieve highly [001]-oriented PrAlO3 films on SrTiO3 (001) by SPE at a
relatively low annealing temperature, at which PrAlO3 films on SiO2/Si remain
amorphous.
 University of Wisconsin-Madison: P. Zuo,
T. F. Kuech, S. E. Babcock, P. G. Evans
 Wayne State University: W. Waduge, C.
H. Winter.
 Funding support from
NSF through the
University of Wisconsin
MRSEC (DMR-1720415)
• Y. Chen et al., ACS Appl. Mater.
Interfaces 9, 41034-41042 (2017)
• P. G. Evans et al., Curr. Opin. Solid State
Mater. Sci. 22, 229 (2018)
• Y. Chen et al., J. Phys. Chem. C (2019)
• W. Waduge et al., Solid Phase Epitaxy of
PrAlO3 Films Grown by Atomic Layer
Deposition, In preparation (2019)