Exploring the Limits of Epitaxy
to further
Materials by Design
Darrell G. Schlom
Department of Materials Science and Engineering
Cornell University
Kavli Institute at Cornell for Nanoscale Science
Sandwich Maker
Outline
•  What can be synthesized
–  Ruddlesden Popper (An+1BnO3n+1) with n up to 10
–  Aurivillius (Bi2O2(An–1BnO3n+1)) with n up to 8
–  Superlattices
–  Strain Game with ε11 ≈ ε22 up to 6%
–  Epitaxial Stabilization
–  in situ ARPES
•  Challenges
MBE ≈ Atomic Spray Painting
Ruddlesden-Popper An+1BnO3n+1 with n ≤ 10
n = 10 has 104
atoms in unit cell
C.H. Lee, N.J. Podraza, Y. Zhu,
R.F. Berger, S. Shen, M. Sestak,
R.W. Collins, L.F. Kourkoutis,
J.A. Mundy, H.Q. Wang, Q. Mao,
X.X. Xi, L.J. Brillson, J.B. Neaton,
D.A. Muller, and D.G. Schlom,
Applied Physics Letters 102 (2013)
122901.
n = 8 Aurivillius Phase [Bi4Ti3O12—(SrTiO3)5]
!
!
!
M.A. Zurbuchen, N.J. Podraza, J. Schubert, Y. Jia, and D.G. Schlom,
Applied Physics Letters 100 (2012) 223109. (SrRuO3)1 / (SrTiO3)5 Superlattice
ADF-STEM
2 nm David Muller’s group (Cornell)
STEM-EELS
2 nm Red = Ru Teal = Ti Scanning Transmission Electron Microscopy
c axis
[LaMnO3]6 / [SrMnO3]3
La
Mn
E.J. Monkman, C. Adamo, J.A. Mundy,
D.E. Shai, J.W. Harter, D. Shen, B. Burganov,
D.A. Muller, D.G. Schlom, and K.M. Shen,
Nature Materials 11, 855-859 (2012)
Ti
Eric
Monkman
Carolina
Adamo
Julia Mundy,
Muller Group
0
10
*
0010
20
30
40
2θ (degrees)
m=4
*
*
0017
0020
0016
0015
0018
0017
n=6
50
n=5
n=4
*
n=3
n=2
*
0
10
20 30 40
2θ (degrees)
0029
0015
0016
0017
0018
0019
0020
0021
0022
0023
0024
0025
0026
002
0010
0034
0028
0033
0032
0028
0031
0032
0030
0020
0021
0022
0023
0024
0025
0026
0015
003
002
0034
0028
0029
0030
0016
0031
0032
0033
0026
0024
0023
0012
0011
002
0013
0014
0015
0017
0018
0012
004
0019
0027
005
006
007
008
009
0010
0011
0029
002
0011
0012
0013
0014
004
0016
0017
0018
0019
0020
0021
0022
0023
0024
0025
0026
0027
0014
006
007
008
009
005
003
0021
0027
0020
0019
0019
0020
0021
0022
0018
0016
0017
0010
0013
0014
0015
008
009
0010
006
007
n=8
0027
003
Intensity (arbitrary units)
0022
0018
0017
0016
0015
0019
0016
0015
0014
0013
0012
0014
0013
003
004
005
001
009
002
0011
007
008
009
003
004
006
005
008
0010
0012
0011
003
001
*
0015
0018
0014
0013
0014
0013
0012
0011
0010
009
008
007
007
006
005
004
002
*
0031
0012
0012
*
*
0030
*
0011
0011
0010
009
008
007
006
006
005
*
0013
0010
006
005
004
003
002
001
*
004
005
006
007
008
009
0010
0011
0012
0013
009
009
008
007
005
004
004
003
002
001
*
0011
008
007
005
003
002
001
*
006
004
003
002
001
Intensity (arbitrary units)
XRD of (BaTiO3)n / (SrTiO3)m Superlattices
n=3
n=1
n=2
n=1
50
m = 13
A. Soukiassian, W. Tian, V. Vaithyanathan, J.H. Haeni, L.Q. Chen, X.X. Xi, D.G. Schlom, D.A. Tenne, H.P. Sun, X.Q. Pan,
K.J. Choi, C.B. Eom, Y.L. Li, Q.X. Jia, C. Constantin, R.M. Feenstra, M. Bernhagen, P. Reiche, and R. Uecker,
Journal of Materials Research 23 (2008) 1417-1432. The
Game
Strained (001) Perovskite Films
Intensity (arbitrary units)
Substrate
KTaO - 10nm
3
ε11 ≈ ε11 ≤ 3% typical
max to date 6.6% in BiFeO3
SmScO - 20nm
3
EuScO - 20nm
3
GdScO - 20nm
3
TbScO - 20nm
3
DyScO - 20nm
3
SrTiO - 100nm
3
LSAT- 20nm
NdGaO - 20nm
3
NSAT - 20nm
LaAlO - 10nm
3
44 45 46 47 48 49
2θ (degrees)
R.J. Zeches, M.D. Rossell, J.X. Zhang, A.J. Hatt,
Q. He, C.-H. Yang, A. Kumar, C.H. Wang, A.
Melville, C. Adamo, G. Sheng, Y.-H. Chu, J.F.
Ihlefeld, R. Erni, C. Ederer, V. Gopalan, L.Q.
Chen, D.G. Schlom, N.A. Spaldin, L.W. Martin,
and R. Ramesh, Science 326 (2009) 977-980 .
MBE + ARPES
Angle-Resolved
Photoemission
Spectroscopy
(Kyle Shen)
ARPES of LaNiO3: eg Fermi Surface
dx2-y2
hole pockets
0.8 DFT simulation
0.6
0.4
0.2
ky (Å-1)
0.0
-0.2
-0.8
0.8 DFT
0.6 simulation
0.4
0.2
ky (Å-1)
0.0
-0.2
-0.8
ARPES He I
-0.4
0.0
kx (Å-1)
0.4
0.8
0.4
0.8
ARPES He II
-0.4
0.0
kx (Å-1)
d3z2-r2
electron pocket
Giant Quasiparticle Mass Renormalization
0.0
electron-electron
interactions
E-EF (eV)
-0.1
-0.2 max
-0.3
-0.4
Density-functional
theory
min
-0.5
-0.4
-0.2
0.0
-1
k|| (Å )
0.2
0.4
Outline
•  What can be done
•  Challenges
–  Substrates (isostructural, high perfection, desired lattice constant, desired octahedral rotations, …)
–  Substrate Termination
–  Details of Growth Richer than Simple Cartoon
–  Point Defects (including defect complexes)
Commercial Perovskite Substrates
Reinhard Uecker’s Group
Leibniz Institute
for Crystal Growth
Berlin, Germany
Pyrochlore Substrates
Bi2Ru2O7
Y2Ir2O7
Film lattice (Å)
10.0
10.1
Eu2Ir2O7 Bi2Ir2O7 Nd2Ir2O7
10.2
10.3
Bi2Sn2O7
10.4
10.5
10.6
10.7
10.8
Pr2Zr2O7
Lu2Ti2O7
Y2Ti2O7
Eu2Ti2O7
Y4Nb3O12
Gd4Nb3O12
Sm2Ti2O7
La4Nb3O12
Nd4Nb3O12
Substrate lattice (Å)
•  New, large Sm2Ti2O7
crystals (Czochralski)
•  Suitable for fabrication of
1 cm x 1 cm substrates
•  Annealing in O2 removes
oxygen vacancies
Floating zone furnace
(Augsburg)
AFM: as-polished (111) Sm2Ti2O7
(floating zone)
Collaboration with University of Augsburg (Jochen Mannhart’s Group), Leibniz Institute for Crystal Growth (Reinhard Uecker’s Group) and Johns Hopkins University (Tyrel McQueen’s Group)
•  (100) and (111) SrTiO3
G. Koster, B.L. Kropman, G.J.H.M. Rijnders,
D.H.A. Blank, H. Rogalla, “Quasi-Ideal Strontium
Titanate Crystal Surfaces through Formation of
Strontium Hydroxide,” Applied Physics Letters 73
(1998) 2920-2922. •  (110) REScO3
J.E. Kleibeuker, G. Koster, W. Siemons,
D. Dubbink, B. Kuiper, J.L. Blok, C-H. Yang,
J. Ravichandran, R. Ramesh, J.E. ten Elshof,
D.H.A. Blank, and G. Rijnders, “Atomically
Defined Rare-Earth Scandate Crystal Surfaces,”
Advanced Materials 20 (2010) 3490-3496.
•  (100)p and (111)p LaAlO3
J.L. Blok, X. Wan, G. Koster, D.H.A. Blank, and
G. Rijnders, “Epitaxial Oxide Growth on Polar
(111) Surfaces ,” Applied Physics Letters 99 (2011)
151917 .
AFM (100) SrTiO3—Jochen Mannhart
Surface Termination Recipes
RHEED Intensity (arb. units)
[110] azimuth
Terminated vs. Unterminated SrTiO3 (BaTiO )
3 4
(SrTiO ) (BaTiO3)4 (SrTiO ) (BaTiO )
3 2
3 2
3 4
(SrTiO )
3 2
Ti shutter open
Not
Terminated
Sr shutter open
Ba shutter open
0
200
400
600
800
RHEED Intensity (arb. units)
[100] azimuth
Time (s)
Ti shutter open
Terminated
Ba shutter open
0
100
200
Sr shutter open
300
400
Time (s)
500
600
700
Terminated vs. Unterminated DyScO3 (SrTiO )
3 4
3 8
RHEED Intensity (arb. units)
[110] azimuth
(BaTiO )
Ti shutter open
Not
Terminated
Sr shutter open
Ba shutter open
0
100
200
300
400
Time (sec.)
(SrTiO )
3 4
3 8
RHEED Intensity (arb. units)
[110] azimuth
(BaTiO )
Ti shutter open
Terminated
Ba shutter open
0
100
200
Sr shutter open
300
Time (sec.)
400
500
Ti shutter open
RHEED Intensity (arb. un.)
[110] azimuth
Terminated vs. Unterminated GdScO3 Not
Terminated
Ba shutter open
0
200
Sr shutter open
400
600
800
Time (sec.)
3 8
RHEED Intensity (arb. units)
[110] azimuth
(BaTiO )
(SrTiO )
3 4
(BaTiO )
3 8
(SrTiO )
3 4
Ti shutter open
Terminated
Ba shutter open
0
200
Sr shutter open
400
Time (sec.)
600
800
n=2
n=3
n=6
? substrate
5 nm
10 nm
In each case, the first SrO fault is missing – independent of n!
12 layers of SrTiO3
TiO2
SrO
TiO2
SrO
TiO2
SrO
TiO2
SrO
TiO2
SrO
TiO2
SrO
SrO
TiO2
SrO
TiO2
SrO
TiO2
SrO
TiO2
SrO
TiO2
SrO
TiO2
SrO
6 SrTiO3
Unit Cells
Additional
SrO layer is
missing!
6 SrTiO3
Unit Cells
6 layers of SrTiO3
TiO2
SrO
TiO2
SrO
TiO2
SrO
TiO2
SrO
TiO2
SrO
TiO2
SrO
SrO
TiO2
SrO
TiO2
SrO
TiO2
SrO
TiO2
SrO
TiO2
SrO
TiO2
SrO
SrO
6 SrTiO3
Unit Cells
1 SrO Layer
6 SrTiO3
Unit Cells
Initial SrO
layer
Unstable double SrO layer [110] Azimuth SrO SrO . . . TiO2 SrO SrO . . . SrO TiO2 SrO . . . SrO SrO SrO . . . TiO2 SrO SrO SrO . . . SrO TiO2 SrO SrO . . . 3 layers of SrO is needed in forming double Sr layer [110] Azimuth Oxide MBE + ARPES Team