2011/12/14 2nd term m1 colloquium creation of huge metal-insulator domain and its electrical...
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2011/12/14 2nd term M1 colloquium
Creation of huge metal-insulator domainand its electrical conduction propertyin VO2 thin film on TiO2(001) substrate
Tanaka Laboratory
Kenichi Kawatani
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contents
My research・ experimental method・ optical microscope images・ temperature dependence of resistivity
conclusion
Background・ strongly correlated electron system・ vanadium dioxide (VO2)・ phase separation (domain)
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Strongly Correlated Electron System
High-temperature superconductivity Colossal Magnetoresistance
They have very attractive physical properties.
Masatoshi Imada et al.Reviews of Modern Physics,Vol. 70, No. 4, October 1998
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Metal-insulator transition in VO2
Junqiao Wu et al.Nano Lett., Vol. 6, No. 10, 2006
Temperature dependence of resistance in VO2 nanowire
Resistance change so large (about 3 orders of magnitude)
heating
Cooling
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heating
Phase transition ~water~
temperature
ice
ice + water
water
Phase separate around transition temperature.
0℃
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Phase transition ~VO2~
SNIM images of VO2 around transition temperatureM. M. Qazilbash et al. Science 318, 1750 (2007)
In the nano-scale region,insulator and metal phases separated around transition temperature.
lnsulator Metal
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Purpose of my research
Metal
I research about phase separation in VO2.
I want to observe each electronic phase’s behavior.
Insulator
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Experimental condition
Cr/PtVO2
Substrate
Film thickness 30nmFilm size 50×50μm2
Substrate TiO2(001)
Sample condition Equipment
PPMS(Physical Property Measurement System)
temperature dependenceof resistance
Optical microscope
observe domain
Temperature controller
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Temperature dependence of resistivity
VO2 turn from insulator to metal around 300K.
0.1
2
46
1
2
46
10
2
46
100
Res
isti
vity
(oh
m c
m)
315310305300295290285Temperature (K)
Phasecoexistence
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Huge metal-insulator domain
Optical microscope images at heating VO2 (290K to 310K)
VO2 color changed. VO2 turned from insulator to metal.
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290K
10μm
Insulator
293K
10μmMetal domain
Huge metal-insulator domain
Metal-insulator domain size is so large.
past one
Optical microscope image of VO2
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Strain from substrate
crystal VO2 TiO2
a-axis length 0.455 0.459
Lattice mismatch(%) - 0.863
VO2 on TiO2(001) is affected by strain from substrate.
Lattice parameter of each material
Huge domain was caused by strain.
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Resistivity jumps
Temperature dependence of resistivity in detail (heating)
Resistivity change discretely.
0.1
2
46
1
2
46
10
2
46
100
Res
isti
vity
(oh
m c
m)
315310305300295290285Temperature (K)
50
45
40
35
30
25
20R
esis
tivity
(oh
m c
m)
298.0297.8297.6297.4297.2297.0Temperature (K)
1st2nd
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Jumps meaning
Resistivity changes. Insulator domain turn to metal.
290K
10μm
293K
10μm
What do jumps means?
Metal domain
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One domain’s behavior
2
2
)()(
)()(
dLLd
d
TR
TTRTR
][17~10 md
Same with optical microscope image
Relation betweenresistivity jump and domain size
To evaluate domain size,
R(T) R(T+ΔT)
Insulator
Metal
L × L μm2
d× d μm2
A
B
RA
RB
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One domain’s behavior
50
45
40
35
30
25
20
Res
istiv
ity (
ohm
cm
)
298.0297.8297.6297.4297.2297.0Temperature (K)
1st2nd 293K
10μm
Resistivity jumps Each domain’s behavior
I could observe one domain’s behavior as resistivity jumps.
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Control of each electronic phase
1.0x105
0.8
0.6
0.4
0.2
0.0
Res
ista
nce(
ohm
)
6543210Voltage(V)
1st2nd3rd
46
104
2
46
105
2
46
106
2
Res
ista
nce(
ohm
)
320310300290280Temperature(K)
Voltage dependence of resistance
We want to control each electronic phase by electric field.
290K
10μm 293K
10μm
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Conclusion
I fabricated VO2 thin films on TiO2(001).
・ huge domain caused by strain
・ resistivity jumps one domain’s behavior
293K
10μm
50
45
40
35
30
25
20R
esis
tivi
ty (
ohm
cm
)
298.0297.8297.6297.4297.2297.0Temperature (K)
1st2nd
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Resistivity jump
50
45
40
35
30
25
20
Res
isti
vity
(oh
m c
m)
298.0297.8297.6297.4297.2297.0Temperature (K)
1st2nd
7.0x10-2
6.5
6.0
5.5
5.0
4.5
4.0
Res
isti
vity
(oh
m c
m)
340.0339.8339.6339.4339.2339.0Temperature (K)
1st2nd
TiO2(001) Al2O3(0001)
Temperature dependence of resistivity in detail (heating)
Resistivity in VO2 on TiO2(001) change discretely.
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Resistance susceptivity
14
12
10
8
6
4
2
0
Cha
nge
rate
(%
)
298.0297.8297.6297.4297.2297.0Temperature (K)
1st2nd
14
12
10
8
6
4
2
0
Cha
nge
rate
(%
)
340.0339.8339.6339.4339.2339.0Temperature (K)
1st2nd
1.0
0.8
0.6
0.4
0.2
0.0
Cha
nge
rate
(%
)
340.0339.8339.6339.4339.2339.0Temperature (K)
Change rate 100)(
)()()(
TR
TTRTRT
Change rate of VO2 on TiO2(001) is 30 times bigger than Al2O3(0001) one.
TiO2(001) Al2O3(0001)
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Title