stuart.lindsay@asu.edu interfacing molecules to electronic materials
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Stuart.Lindsay@ASU.EDU
Interfacing Molecules to Interfacing Molecules to Electronic MaterialsElectronic Materials
Artificial EnzymesArtificial EnzymesHydrogen generation, photovoltaicsHydrogen generation, photovoltaics
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Steinberg-Yfrach et al. Nature 392, 479 (1998)
1. Make functional molecules
2. Wire molecules to electrodes
Steps to bio/molecular electronics:Steps to bio/molecular electronics:
3. Make them function on electrodes like they do in solution
4. Make economically-viable devices
Test Case: Single Molecule SwitchTest Case: Single Molecule Switchmade from Oligo Anilinemade from Oligo Aniline
HS
HN
NH
HN
NH
HN
NH
HN
SH
Insulatori
VConductor
-2e-
Insulator
-2e-
Single Molecule Switch?
Molecular electronics vs. solution Molecular electronics vs. solution charge transfer chemistrycharge transfer chemistry
• Charge transfer in nature in solution + ions.
• Charge transfer in molecular electronics electrode to electrode – No water/ions
12
LUMO
HOMO
CHARGED
Why solvent + ions matterWhy solvent + ions matter
e-
EN
ER
GY
e-
LANDAUER
MARCUS
SS
Charge Transfer in DNACharge Transfer in DNA
Barnett et al., Science 294 567 (2001)
The ChallengeThe Challenge
Need to measure single molecule conductance in a conducting solution with independent control of charge state.
How to do this?
0.000 0.005 0.010 0.015 0.020
0.0
0.2
0.4
0.6
0.8
1.0
0.0 0.4 0.8 1.2 1.60
2
4
6
Current (nA
)
G (
10-5X
2e2 /h
)
Time (Second)
Distance (nm)
Repeated break junctionRepeated break junction
Xu and Tao, Science 301, 1221-1223 (2003)
Wiring Single Molecules ReliablyWiring Single Molecules Reliably
Cui et al. Science 274 571 (2001)
Xu and Tao, Science 301 1221 (2003)
GOOD NEWS: 7000:1 G range – worst Gtheor/Gmeas is 3.3
BAD NEWS: All Landauer theory
Operating probes in electrolyteOperating probes in electrolyte
Rev. Sci. Instrum. 60, 3128 - 3130 (1989)
(DNA - Xu et al. Nanoletts 4 1105 2004)
Insulating layer
Controlling ion gradients/electric Controlling ion gradients/electric fields at an electrode surfacefields at an electrode surface
Bigger ion gradient = Bigger electric field at molecule
Measuring transport as a function Measuring transport as a function of oxidation stateof oxidation state
H NH N
O
H NHN
OH N
H NO
HNHN
O
H NH N
O
H NH N
OH N
H NO
HNHN
O
O
O +-
Es
Vts
LOCAL FIELD
SURFACE FIELD
-0.2 0 0.2 0.4 0.6 0.8
Electrochem
ical Current
Surface Potential, ES , V vs. Ag
-0.2 0 0.2 0.4 0.6 0.80
1
2
3
4
5
6
7M
olec
ular
Con
duct
ance
(nS
)
-0.2 0 0.2 0.4 0.6 0.8
G=GMAX- a(ES-b)2
Insulator Conductor Insulator
TIP-SUBSTRATE V FIXED AT 50mV
-0.2 0 0.2 0.4 0.6 0.8
Ofer et al. JACS 112 7869, 1990
0
0.1
0.2
0.3
0.4
0.5
0.6
0 0.1 0.2 0.3 0.4 0.5 0.6
Neutral molecule
- - - - - -
Cur
rent
(nA
)
Tip-substrate bias (V)
(NO IONS)
FIX ES, VARY TIP FIELD
Oxidized molecule ES=0.4V(H2SO4)
0
0.1
0.2
0.3
0.4
0.5
0.6
0 0.1 0.2 0.3 0.4 0.5 0.6v
G=Gmax-a(ES-b)2
ES(V) =ES-V
v
=1.4
v
ES=0.3VES=0.25V
Tip-substrate bias (V)
Cur
rent
(nA
)
- - - - - -
MOLECULE FIELD = SURFACE FIELD ± TIP FIELD
We have a two terminal switch!
Vi
i
Vi
i
Vo
Vo
i
Vo
iA B
Vi
0 0.1 0.2 0.3
0
0.2
0.4
0.6
0.2 0.3 0.4 0.5 0.6
0.5
1.0
0.2 0.3 0.4 0.5 0.6
0.4
0.8
Cu
rre
nt (
nA
)
Vts (Volts) ES (V vs. Ag Wire)
- - -
But it will need more than one But it will need more than one molecule:molecule:
Bias sweeps Potential sweeps
SummarySummary
• Made a low-voltage switch based on chemical knowledge, get NDR
• Probe role of fluctuations
• Roadmap for going from chemistry to molecular electronics
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