Strain Energy Released by forming edge dislocations ... Surface Terrace Induced
Strain in Epitaxial Films d. Δd. APB .... strain and improved by tensile strain.
Interfaces in Advanced Materials – A Key Role for Active Device Application
Chonglin Chen Department of Physics, University of Texas at San Antonio, Texas
[email protected]
• Introduction • Interface in Epitaxial Ferroic Thin Films • Surface-Step-Terrace Induced Nano Domain Structures • Giant MR Effects in Ferromagnetic Manganite La1-xCaxMnO3 thin Films • Summary
Acknowledgements Collaborations: Z. Yuan, J. Weaver, S. Liu, Y. Lin,* L. Chen,* and X. Chen* – Oxide Thin Film & Nanostructure Lab. A. J. Jacobson, W. Donnor –University of Houston J. C. Jiang -- Louisiana State University E. I. Meletis – University of Texas at Arlington Q. X. Jia -- Los Alamos National Laboratory W. Chang – Naval Research Laboratory X. H. Chen -- Univ. Sci. Tech. China, Hefei, P. R. China C. L. Jia, and K. Urban -- Institut Fur Festk. (IFF), Germany
Sponsors: The State of Texas National Science Foundation Department of Energy
Neumann’s Principle and Heckmann Diagram at Interfaces The symmetry elements of any physical property of a crystal must include the symmetry elements of the point group of the crystal.
• Symmetry • Dimensions • Strain • Unbalanced Charge • Quantum Effects • Many others
Real Surface Structures Chen & Tsong, PRB (1988)
(001) SrTiO3
200 nm
After annealing
BO2 Terminated
AO Terminated
Perovskite ABO3
A
B
O
200 nm Chen PRL (1994), SS (1998)
Charge in Interface 1017/cm2
Basic Concepts of Epitaxy film
substrate
Commensurate Growth (homoepitaxy)
Heteroepitaxial Growth Chen, PLD Principles & Appl. (2006)
Strain Energy Released by forming edge dislocations The strained film said: “We are all tired enough, please give us a break!”
Oh, it is much comfortable, although a few of our colleagues are still suffering the pressure.
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Strain energy released
af
>
as
The single said: “It is OK, my effort is to make all of you happy!” Chen, PLD Principles & Appl. (2006)
Surface Terrace Induced Strain in Epitaxial Films Δd
d APB
Strained Domain
APB
Science (submitted)
Highly Epitaxial growth of SrRuO3 film on (001) SrTiO3 2θ
Intensity (x103)
2.5
20
30
40
50
2.0
60
(002)STO
1.5 1.0 (004)SRO
0.5
Intensity (x103)
0.0 40 20
(002)STO
STO
(004)SRO
30
o
0.094
0.091o
20
10
10 0
0 23
24
22
θ
23
STO
24
θ
100 nm 2.0 1.5 1.0
8
2 MeV He+ RBS-Channeling Spectra
χmin = 2.2%
0.0
Ru surface
Random
4
0
50
100
150
200
Distance (nm)
Ru interface
250
400
1
300
2
ρ (μΩcm)
Counts (x1000)
6
0.5
2
Aligned x 3 0 150
200
250
300
350
200
As grown 3x10 15 /cm 2 9x10 15 /cm 2 2.5x10 16/cm 2 4.0x10 16/cm 2 6.0x10 16/cm 2
100
Channel 0 0
50
100
150
200
250
300
T (K)
Chen, et al., APL (1997)
(Ba,Sr)TiO3 Thin Films on (001) LaAlO3
Ferroelectric BSTO (50:50) on (001) LaAlO3
Chen et al., APL (2002)
Cross-section TEM of Ba0.6Sr0.4TiO3 films on (001) MgO
Ba0.6Sr0.4TiO3
(a)
MgO
2 nm
Ba0.6Sr0.4TiO3
(b)
MgO
(a) HRTEM of the cross-sectional Ba0.6Sr0.4TiO3 / MgO showing a sharp interface. (b) Fourier filtered showing misfit dislocations at the interface. Jiang & Chen JAP (2002)
Mn:BSTO Films on (001) MgO
4.0 3.5 3.0
ε = 1200 Tan δ = 0.005 @ 12.84 GHz & RT
2.5 2.0 1.5 1.0
tunability = 80% -8
-4
0
4
8
Field (V/μm)
2000
0.1
0.08 1500 0.06 1000 0.04 500 0.02
0
0 15
20
25
Frequency (GHz)
APL. (Oct 10, 2005)
30
Loss-tangent
0.5
Relative Dielectric Constant
Dielectric constant (x1000)
Mn:BSTO (60:40) films on (001) MgO
Cross Sectional TEM Studies of PSTO
(a)
(b)
(e)
(c)
(d)
Dielectric Constants of PSTO Films 4500
Films
Tetrago nality
εr
Tuna bilty
PSTO on LAO
-0.11%
3100
48%
0.008
PSTO on NGO
-0.25%
4300
59%
0.01
[100 ] PSTO on NGO
0.51%
2033
48%
--
[010 ] PSTO on NGO
0.97%
1634
33%
--
Loss Tangent
Dielectric Constant
4000
PSTO on NGO
3500
Along PSTO [010] on NGO,Slow cooling
3000
PSTO on LAO
2500 2000 1500
PSTO [100] ]on NGO,slow cooling
1000 -60
-40
-20
0
20
40
60
Electric Field (kV/cm) Measured at 1MHz and room temperature by interdigital technique
• Dielectric constant and tunability tend to be reduced by compressive strain and improved by tensile strain. PRL. (submitted)
Dielectric Tunability of (Pb,Sr)TiO3 Thin Films 0.62
1.15 1.10
0.245 GHz 2.195 GHz 4.995 GHz 10.04 GHz 14.99 GHz 20 GHz
1.00 0.95
0.60 0.58
0.90
Tunability
Room Temperature Capacitance
1.05
0.85 0.80 0.75 0.70 0.65
0.56 0.54 0.52 0.50
0.60 0.55
0.48
0.50 -30
-20
-10
0
10
Voltage (V)
20
30
40
50
0
5
10
15
20
Frequency (GHz)
APL. (Oct 3, 2005)
Surface-Step-Terrace Induced Nanodomain Structures
Cross-section TEM of Ba0.6Sr0.4TiO3 films on (001) MgO
Ba0.6Sr0.4TiO3
(a)
MgO
100 nm
10 nm
Dark-field image of a common reflection showing periodically distributed dislocations at the interface.
Jiang & Chen JAP (2002)
Anti-Phase Domain Structure
APB (b)
2 nm
1 nm
HRTEM image of the BSTO/MgO interface showing that the antiphase boundaries start from the steps on the surface.
(c) Jiang & Chen JAP (2002)
Surface-Step-Terrace Induced Anti-Domain Structures [001]
[010]
I
1
A
II
K
2
III (c)
B
(a)
[100] NC-APB
C-APB
1 2
(b)
(d)
TEM images of Epitaxial Behavior of BSTO/LAO
Gao & Chen APL (1999); Chen APL (2002)
Measured with HP8510C Network Analyzer & Microwave Probe Calculated C & Q (0V and 40V DC Bias) from 0.5 GHz to 10 GHz #082102, MgO(1°off)
#082302, MgO(3°off)
0.4
40 V
0.5
150
0.2
40 V
0V
0.4
40 V
0.3
100
0.2
40 V
50
0.1
150
40 V 0.3
100 0.2
0V 4
6
8
0V
0.0 2
Frequency (GHz)
50
40 V
0.1
0V 0 10
150
0.4
50
0.1
0.0
0V
Q
100
0.5
Q
0.3
2
200
Capacitance (pF)
0V
200
Capacitance (pF)
0.5
Q
Capacitance (pF)
200
#082502, MgO(5°off)
4
6
8
0 10
0.0 2
Frequency (GHz)
4
6
8
0 10
Frequency (GHz)
Calculated C, εr & Q (0V and 40V DC Bias) at 2 GHz
Sample #
Gap Length (μm)
Gap Width (μm)
Film Thick. (μm)
C0V (pF)
εr (0V)
Q0V
C40V (pF)
εr (40V)
Q40V
Cap Tuning (40V)
εr Tuning (40V)
#082102 MgO (010, 1° off) #082302 MgO (010, 3° off) #082502 MgO (010, 5° off)
762
6
0.3
0.463
1028
24
0.351
682
54
24 %
34 %
762
6
0.3
0.386
790
32
0.324
598
60
16 %
24 %
762
6
0.3
0.519
1202
22
0.386
790
48
26 %
34 %
Ferroelectric BSTO (60:40) thin film on miscut (001) MgO substrates: UH Data #2
Measured with HP8510C Network Analyzer & Microwave Probe Calculated C & Q (0V and 40V DC Bias) from 0.5 GHz to 10 GHz
0V
0.8
70
0.6
60 0.6
40 0.2
40 V
30
0.0
70
0.8
60 0.4
40 V
0.2
50 40
0.0 30
40 V
-0.2
0V
1.0
0V
20 -0.2
80
10
-0.4
0
-0.6
80 70
0V
60 0.6
40 V
50
Q
50
0.4
MgO (5°off), #053102
Q
40 V
Q
Capacitance (pF)
0.8
80
Capacitance (pF)
1.0
MgO(3°off), #052902
Capacitance (pF)
MgO(1°off), #052402
0.4 40 0.2 30
40 V
0.0
20
20 10
-0.2
0
-0.4
0V
10
0V -0.4 2
4
6
8
10
2
Frequency (GHz)
4
6
8
0 2
10
Frequency (GHz)
4
6
MgO (010, 1° off) #052402 - 300 nm MgO (010, 3° off) #052902 - 300 nm MgO (010, 5° off) #053102 - 300 nm
10
Frequency (GHz)
Calculated C, εr & Q (0V and 40V DC Bias) at 2 GHz Sample #
8
Gap Length (μm) 762
Gap Width (μm) 5
Film Thick. (μm) 0.3
C0V (pF)
εr (0V)
Q0V
C40V (pF)
εr (40V)
Q40V
Cap Tuning (%)
εr Tuning (%)
0.774
1664
14
0.442
800
35
43 %
52 %
762
6
0.3
0.473
1059
13
0.345
663
23
27 %
37 %
762
4
0.3
0.924
1655
11
0.440
635
26
52 %
62 %
Ferroelectric Mn:BSTO (60:40) thin film on miscut (001) MgO substrates
Microstructures and Interface of BSTO Films on Vicinal (001) MgO
Chen et al, PRL
Dislocation Density and Average Spacing Misfit dislocations can be generated at interface to reduce misfit strain energy. The lattice misfit between substrate and film and the average spacing S of misfit dislocations are defined as: (as − a f ) f = as
S = as / f (001) MgO, 1o off
(001) MgO, 3o off
(001) MgO, 5o off
Calculation Data
6.951 nm
6.951 nm
6.951 nm
Observed Value
6.90 nm
6.54 nm
7.06 nm
Step Wide
120.67 nm
40.22
24.13
Edge Dislocation Number on Step
17.38
5.78
3.47
Chen et al, PRL (Submitted)
Surface Terrace Induced Strain in Epitaxial Films Δd
d APB
Strained Domain
APB
PRL (submitted)
Nano Phase Separation Behavior in CMR Manganites
Ferromagnetic La1-xCaxMnO3
A. P. Ramirez, Cond. Matt., 9 (1997) 8171 A. P. Ramirez, et al., PRL, 75 (1995) 3336
Electrical Properties of La0.67Ca0.33MnO3 -0.2 -0.4 0
-0.6
-200 -400
-0.8 MR (%)
-1.0
-600 -800
-1000 -1200
-1.2
-1400 0
2
4
6
8
10
12
14
H (Tesla)
-1.4 0.07
0
3T 5T 9T 14 T
-2 -4 -6 -8
0 -2
-10 -12
MR (%)x1000
3T 5T 9T 14 T
(ρ(H)-ρ(0))/ρ(H) (%)(x1000)
0.0
La0.67Ca0.33MnO3/STO
-4 -6 -8 -10 -12 -14
-14
-16 0
2
4
6 8 H (Tesla)
10
0.06
0
0.05
0T 0.04
3T
0.03
9T
0.01
14
10
0T 3T 5T 9T 14 T
-1
10
5T
0.02
12
-16
Resistivity (Ω cm)
Resistivity (Ω cm)
(ρ(H)-ρ(0))/ρ(H) (%) (x1000)
La0.67ca0.33MnO3/LAO
14T
-2
10
0.00 0
50
100
150
200
250
Temperature (K)
300
350
0
50
100
150
200
250
Temperature (K)
300
350
Chen, et al., PRB (2004)
Electrical Properties of LCMO on (001) MgO
Resistance ( Ω )
13
1012 1011 1010 10 9 108 107 106 105 104 103 102 101 10
MR effect ratio ~ 1010! 0 T Tc ~ constant! Previous record: ~106
0
3T 5T 6T 6.5 T 7T 8T 10 T 14 T
50 100 150 200 250 300 Temperature ( K )
Chen, et al., Nature (submitted)
Nano-Phase Separation – Nanoscale cluster Models
TEM Image of Epitaxial Behavior of LCMO/MgO
100 nm
Chen, et al., Nature (submitted)
Magnetoresistivity in Nanostructures
d
d
d = d (H ) The transmission wave are
h 2 d 2ϕ ' − + Voϕ ' = Eϕ ' 2 2m dz
KWB method: 1/ 2 μ φ ( / ) i ≡ 6.2 × 10 6 F 2 exp(−6.8 × 10 7 d ) μ +φ
Barrier Transmission rate:
1 T= ( k 2 + k '2 ) 2 2 1+ sinh k'd 2 2 4k k '
k’d>>1
16k 2 k '2 − 2 kd T≅ 2 e 2 (k + k ' ) Chen, et al., Nature (submitted)
Self-Assembly of Oxide Rods/Ribbons/Dots
Microstructures of Nanocolumnar Structures of (La,Sr)MnO3
Jiang & Chen, Nano Lett., (2004)
Magnetization in Magnetic Field and Temperatures 0.0015
0.0018
Epitaxy, 1000 Oe
0.0015 0.0013
0.0012
Magnetization (emu)
0.0010 0.0008
M (emu)
0.0005 0.0003 0.0000 -0.0003 -0.0005
Nanorod , H⊥ Nanorod , H// Epitaxy, H⊥ Epitaxy, H//
-0.0008 -0.0010
Epitaxy, 100 Oe
0.0009
Nanorod, 1000 Oe
0.0006 Nanorod, 100 Oe
0.0003
0.0000
-0.0013 -0.0015 -0.0018 -1000
-0.0003
-500
0
500
1000
H (Oe)
Magnetization hysteresis loops of LMO Films at 5 K in two different magnetic field directions
0
50
100
150
200
250
300
Temperature (K)
Temperature dependent magnetization of the two films in 100 Oe and 1000 Oe applied field for both FCW and FC runs.
Jiang & Chen, NanoLett. (2004)
Self-Assembly of Highly Epitaxial Oxide Nanoribbons GCO (200)
20
30
40
50
T( C)
experimental fitting log (f)
-8
4
-6
ω
5
3 2
6
0 0
2
4
6
8
10 5
Re (Z) (X10 ) Ω
60
19
20
70
500
12
14
nd
0.1
st
GC O/ NG O
on MgO 1 run
E a
0.01
=0 .7 4
eV
eV
-2
600
6 .8 =0 Ea
-4
700
18
on MgO 2 run gO /M CO G
5
-10
800
θ
on NGO
Conductivity σ (s/cm)
-12
Im (Z) (x10 Ω)
900
17
2θ
o
-14
16
NGO(300)
[010]NGO//[02-2]GCO
GCO(200)
NGO(100)
[100]NGO//[100]GCO
15
NGO(200)
14
[001]NGO//[022]GCO
1E-3 0.8
0.9
1.0
1.1
1.2
1.3
1.4
-1
1000/T(K ) Chen et al., Science, submitted
o
GCO(400)
FWHM=0.6
Self-Assembled Nanoribbon Structure of Gd:ZrO
GZO layer 2
GZO layer 1
(a)
(b)
LAO
(c)
(d)
Nanoribbon Structure of Gd:ZrO α
β
GZ O
β '
GZO[010]
GZO[10]
Domain β
GZO[001]
Domain α GZO[110]
GZO[001]
GZO[100]
Domain β’ LAO[010]
LA
(a ) O LAO
α
β
GZO[001]
β'
LAO[100]
GZO[110]
(b )
(c )
(d )
(e )
GZO[10]
Self-Assembly of ZnO Nanorods on SiN Buffered Si
Summary • Interface is a critical topic in advanced material thin films and active device fabrications • New/interesting physical phenomena have been found and achieved in the interface materials • More experimental and theoretical works are needed to explore the interface physics Contact Information: email: phone:
[email protected] (210) 458-6427
