single molecule electronics
DESCRIPTION
Single Molecule Electronics. [email protected] Arizona Biodesign Institute. Single molecules as a tool for understanding. More Single molecules for better understanding. Photosynthesis and single molecule electronics The ASU-Physics-Chemistry-Engineering-Motorola group:. The Program. - PowerPoint PPT PresentationTRANSCRIPT
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Single Molecule ElectronicsSingle Molecule Electronics
Arizona Biodesign Institute
Single molecules as a tool for understanding
More Single molecules for better understanding
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Photosynthesis and single molecule electronicsPhotosynthesis and single molecule electronicsThe ASU-Physics-Chemistry-Engineering-Motorola group:
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Make fixed-gap (useful? T-dep?) devicesMake fixed-gap (useful? T-dep?) devices
The ProgramThe ProgramMeasure Single Molecule in well-defined Measure Single Molecule in well-defined conditionsconditions
Compare with theory (repeat as needed!)Compare with theory (repeat as needed!)
‘‘Calibrated’ molecules and contacts for devicesCalibrated’ molecules and contacts for devices
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Many Few-Molecule-Devices have been made but measurements/theories generally do not
agree: For example, DNA is:
AN INSULATOR (D. Dunlap et al. PNAS 90, 7652, 1993)
A SEMICONDUCTOR (D. Porath et al, Nature 403, 635, 2000)
A CONDUCTOR (Fink and Schoenberger, Nature 398, 407,1999)
A SUPERCONDUCTOR (A.Y. Kasumov et al. Science 291, 280, 2001)
The molecule-metal contact The molecule-metal contact problemproblem
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1.1. Self-assembly: well defined geometry, Self-assembly: well defined geometry, contactscontacts
2.2. Repeated contact (simpler after answer is Repeated contact (simpler after answer is known)known)
3.3. Fixed nano-gaps: problem of Fixed nano-gaps: problem of manufacturabilitymanufacturability
Making Single Molecule Making Single Molecule JunctionsJunctions
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i
Self-assembled Self-assembled nanojunctionnanojunction(Science 294, 571, 2001)
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Alkanedithiols – STM Images
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-40
-30
-20
-10
0
10
20
30
40
-1.0 -0.5 0.0 0.5 1.0
1I(V)
2I(V)
3I(V)
4I(V)
5I(V)
Cur
rent
(nA
)
Tip bias (V)
IV-Curves are integral multiples
-8-6-4-202468
-1.0 -0.5 0.0 0.5 1.0
1I(V)/12I(V)/23I(V)/34I(V)/45I(V)/5
Tip bias (V)
NI(
V )/N
(nA)
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Two Models for ‘quantized ‘ data
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Histogram of curve multipliers
0100200300400500600700
0 1 2 3 4 5Current divisor X
• Find X such that variance from curve to curve is minimized
• Over 1000 curves for n=1
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IV-Curves of bonded molecules not very stress dependent!
-2
0
2
4
6
8
10
10-5
0.0001
0.001
0.01
0.1
1
10
100
-24 -20 -16 -12 -8 -4 0 4F
orce
(n
N)
Current (n
A)
Distance moved (nm)
Current not stress-dependent – through bond?
Mechanical
Bonded
F
IF(h)
(Nanotechnology 13 5-14, 2002)
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0.0001
0.001
0.01
0.1
1
10
100
0 0.2 0.4 0.6 0.8 1
Cur
rent
(n
A)
Tip Bias (V)
Theory Bonded
Mechanical
I is closer to theory for bonded molecules
Comparison with electrochemistry:
)0(2
A
B
EKe
TkR
Tk
E
KEK
B
A
A
exp
)0(
K=105s-1, EA=21kJ/m, R(C8)=300M
R(C8)=950M
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More chain lengths give (V) (J. Phys. Chem. B 106 8609-8614, 2002 )
-0.04
0
0.04
-0.05 0 0.05
-0.02
0
0.02
-0.05 0 0.05
0
50
1 2 3 4
-15
-10
-5
0
5
10
15
-1 -0.5 0 0.5 1
Cur
rent
(nA
)
Tip Bias (V)
-4-3-2-101234
-1 -0.5 0 0.5 1
Cur
rent
(nA
)
Tip Bias (V)
(CH2)10
(CH2)12
0
30
1 2 3 4
• Also measure Ohmic region carefully to get (0)
• Data do NOT agree with theory!
I=I0exp[-(v)z]
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-8
-6
-4
-2
0
2
4
6
8
-1 -0.5 0 0.5 1
Cur
rent
(nA
)
Tip Bias (V)
Clue: I-V doesn’t fit Clue: I-V doesn’t fit tunneling model welltunneling model well
What if the top contact is not so good? Coulomb Blockade?
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Coulomb Blockade: Coulomb Blockade: Quantized charge transferQuantized charge transfer
R1>>h/2e2
Coulomb Blockade
n
n
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-12
-8
-4
0
4
8
12
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
Cur
ren
t (n
A)
Tip Bias (V)
C8
-6
-4
-2
0
2
4
6
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
Cur
ren
t (n
A)
Tip Bias (V)
C10
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
Cur
ren
t (n
A)
Tip Bias (V)
C12
r1 = 1M
c1 = 0.318aF
(from fitting C8)
r8 = 128.36M
r10 = 252M
r12 = 875M
(c1, r1 fixed)
C8=c10 =c12= 0.085aF
(Theory=0.08aF)
Coulomb Blockade fitsCoulomb Blockade fits
(Removes Beta anomaly)(Removes Beta anomaly)
Good agreement for I,
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- Carotene- Carotene
- Phenylene-ethylenine oligomers- Phenylene-ethylenine oligomers
--Technique reveals Technique reveals mobilitymobility of Au of Au contactscontacts
Other MeasurementsOther Measurements
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CaroteniodCaroteniod
SH
HS
32 Å
t
TRANS
CIS
T/C=4:1
(J. Phys. Chem. B, 107, 6162-6169, 2003)
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-10
-5
0
5
10
-1.5 -1 -0.5 0 0.5 1 1.5
Cur
ren
t (n
A)
Tip Bias (V)
-0.2
0
0.2
-0.2 0 0.2-3
-2
-1
0
1
2
3
-1.5 -1 -0.5 0 0.5 1 1.5
Cur
ren
t (n
A)
Tip Bias (V)
a b
R1 R2
C1 C2
Trans
Cis
Measured
No ‘free’ parameters
Simple Tunneling with Simple Tunneling with Coulomb Blockade fits wellCoulomb Blockade fits well
Carotene easily oxidized but vibronic contribution not dominant
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Phenylene-ethylynene OligomersPhenylene-ethylynene Oligomers
and Negative Differential and Negative Differential ResistanceResistance
SAc
NO2
AcS
SAcAcS
1 = 1-nitro-2,5-di(phenylethynyl-4´-thioacetyl)benzene2 = 2,5-di(phenylethynyl-4´-thioacetyl)benzene
1
2
Applied Physics Letters 81 3043-3045 (2002)
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-1.5
-1
-0.5
0
0.5
1
1.5
-1.5 -1 -0.5 0 0.5 1 1.5
Cur
rent
(nA
)
Tip Bias (V)
Single Molecule NDRSingle Molecule NDR
1.8G
50G
1
202468
1012
0 0.5 1 1.5 2
Co
un
t
Peak Volts
Confirms NDR but see non-reversible behavior
Asymmetry, but molecules NOT oriented?
c.f. Reichert et al. PRL 88 2002
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Single Molecule Bonding Fluctuations (Science 300 1413, 2002)
• “Stochastic switching” reported for
• We see the same effect in alkane dithiols
• Significant switching with gold sphere attached
NO2
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• Cannot internal electronic changes
• Cannot be top ‘dipping’ into film
• Cannot be bond to sphere breaking
• Rate increases at annealing temperature
• Fluctuations of lower bond
Single Molecule Bonding Single Molecule Bonding Fluctuations – Property of Au-SFluctuations – Property of Au-S
25 60
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Transport in gold-Transport in gold-n-n-alkane-gold fits ab-initio alkane-gold fits ab-initio tunneling calculations well: One molecule, tunneling calculations well: One molecule, well defined environment.well defined environment.
Gold nanocluster introduces Coulomb BlockadeGold nanocluster introduces Coulomb Blockade
Carotene – good agreement with Carotene – good agreement with tunnelingtunneling calculationscalculations
Phenylene-ethylenine oligomers, confirm NDR. Phenylene-ethylenine oligomers, confirm NDR.
Technique reveals Technique reveals mobilitymobility of Au contacts of Au contacts
ConclusionsConclusions
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Break JunctionsBreak Junctions
(Xu and Tao, Science 301, 1221-1223 2003)
- Geometry unknown BUT
- Calibration available AND
- Most common peak appears to be correct
- Much easier than self-assembled junctions
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Single Molecule Conductance from Single Molecule Conductance from Break JunctionsBreak Junctions
1 2 3
PZT
• Are histogram peaks good data points?
• What is the effect of strain?
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Gold filaments stretch – Gold filaments stretch – maximum force ca 1nNmaximum force ca 1nN
Xu, Xiao, Tao, JACS 2003
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Alkanedithiols:Alkanedithiols:SHHS
RC6=10.5 M
HS SH
N=6:
N=8:
RC8=51 M
SHHSN=10:
RC10=630 M
Major peaks are right peaks
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200nm200nm
SiO2
AuAu
1um
500nm
a b
c
d
2um
e
Fixed Gaps: Fixed Gaps: EBL, Electrochemistry, ElectromigrationEBL, Electrochemistry, Electromigration
Kubatkin et al. (2003) – (but 3 devices/paper)
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Our Fixed Gaps: 10% “Success Our Fixed Gaps: 10% “Success Rate”? Rate”?
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5-20-10
0102030405060708090
77K
Cu
rre
nt(u
A)
SDbias(V)
Vg=-0.5V Vg=-0.25V Vg=0V Vg=0.25V Vg=0.5V
Molecule free molecular transistorMolecule free molecular transistor
Atomic-scale control needed!
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1.1. Measurements and theory in good agreement Measurements and theory in good agreement for some (single) moleculesfor some (single) molecules
(n-alkanes, carotenes, BDT (n-alkanes, carotenes, BDT [Tao, nanolets [Tao, nanolets 44 267] 267]))
2.2. Break junctions can give good data and are Break junctions can give good data and are much simplermuch simpler
Summary 1:Summary 1:
What we think we knowWhat we think we know
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1.1. Single MoleculeSingle Molecule devices need to be devices need to be assembled with assembled with Atomic Precision!Atomic Precision!
2.2. Fluctuations at room temperature?Fluctuations at room temperature?
3.3. Couplings and molecular vs. contact Couplings and molecular vs. contact properties?properties?
4.4. Redox activity molecules and environment?Redox activity molecules and environment?
Summary 2:Summary 2:
What we don’t know/Can’t doWhat we don’t know/Can’t do
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ACKNOWLEGEMENTSACKNOWLEGEMENTSASU PHYSICSXiadong CuiOtto SankeyJohn TomfohrJun LiJin HeASU EngineeringNongjian TaoASU ChemistryAna MooreTom MooreDevens GustXristo ZarateAlex PrimakYuichi TerazanoMotorolaGary HarrisLarry Nagahara