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Experimental characterization of simple single-molecule junctions
2
In collaboration with ...
Leiden: Marc van Hemert
IBM Yorktown Heights: Norton Lang
Technical University of Denmark: Kristian Thygesen, Karsten Jacobsen.
Kamerlingh Onnes Laboratory, Leiden University
Darko Djukic Yves Noat Roel Smit Carlos Untiedt & JvR
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Mechanically Controllable Break Junction
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Mechanically Controllable Break Junction
5
0 50 100 150 200 250 300012345678
Gold, 4.2 K
Con
duct
ance
(2e
2 /h)
Piezo-voltage (V)
6
Conductance histogram for Au
0 1 2 3 40
10
20
30
40
50
G [2e2/h]
# po
ints
(x
103 )
7
Conductance curve for Pt
0.0 2.0 4.0 6.00
1
2
3
4
5
Pt
C
ondu
ctan
ce (
2e2 /h
)
Piezovoltage (V)0.0 2.0 4.0 6.00
1
2
3
4
5
Pt
C
ondu
ctan
ce (
2e2 /h
)
Piezovoltage (V)
8
Conductance histogram for Pt
0 1 2 3 4 5 6 7 80.0
0.2
0.4
0.6
0.8
Pt
N
um
be
r o
f co
un
ts
Conductance (2e2/h)
9
Conductance curve for Pt/H2
0.0 2.0 4.0 6.00
1
2
3
4
5
Pt/H2
Pt
C
ondu
ctan
ce (
2e2 /h
)
Piezovoltage (V)
10
0 1 2 3 4 5 6 7 80.0
0.2
0.4
0.6
0.8Pt/H
2
Pt
N
umb
er o
f cou
nts
Conductance (2e2/h)
Conductance histogram for Pt/H2
Bias voltage 140 mV
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E
eV
k
G decreases for eV > ħω
Principle of point contact spectroscopy
12
Point contact spectrum for Pt/H2
Modulation: 1 mV, 7 kHzRecording time: 10 sTemperature: 4.2 K
0,92
0,93
0,94
0,95
-100 -50 0 50 100
-0,04
-0,02
0,00
0,02
0,04
Pt/H2
d
I/dV
(2e
2 /h)
63.5 mV
- 63.5 mV
dG
/dV
(a.
u.)
Bias voltage (mV)
13
Isotope shift
30 40 50 60 70 800
1
2
3
4
5
6
7
8
9
10Pt + HD
Pt + D2
Pt + H2
Cou
nts
Vibration mode energy [meV]
35 40 45 50
40 45 50 55 60
45 50 55 60 65 70 750
1
2
3
4
5
6
7
8
9
10
Cou
nts
Vibration mode energy [meV]
Pt-H2 not scaled Pt-D2 by Ö2 Pt-HD by Ö(3/2)
14
Conductance fluctuations: 3 examples
-50 0 501.58
1.60
1.62
1.64
1.66
1.68
1.70
G (
V)
= d
I/dV
(2e
2 /h)
-50 0 50
0.99
1.01
1.03
1.05
1.07
1.09
Bias voltage (mV)
-50 0 500.82
0.84
0.86
0.88
0.90
0.92
0.94
Au
15
Principle of conductance fluctuationsin ballistic contacts
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RMS fluctuations measured for Au
Au
0 1 2 3 40.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
G [2e2/h]
s GV
[Go/
V]
Gold
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Conductance fluctuations
0 10
1000
2000
3000
4000
5000
6000
0
1
2
3
Cou
nts
Conductance (2e2/h)
sG
V
(a.u
.)
T = 0.97 (1)
Smit et al., Nature 419, 906 (2002)
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More frequencies and stretching dependence
-100 -80 -60 -40 -20 0 20 40 60 80 100
0,0
0,92
0,94
0,96 PtH2 (no. 13)
d2 I/d
V2 (
a.u
.)
dI/d
V (
G0)
Energy (meV)
-100-80 -60 -40 -20 0 20 40 60 80 100-0,2
0,0
1,00
1,01
1,02
1,03
d2 I/
dV
2 (a.u
.) d
I/d
V (
G 0)
Energy (meV)
-100 -80 -60 -40 -20 0 20 40 60 80 100
0,0
0,92
0,94
0,96 PtH2 (no. 14, stretched no.13)
d2 I/d
V2 (
a.u
.)
d
I/dV
(G
0)
Energy (meV)
-100-80 -60 -40 -20 0 20 40 60 80 100
-0,1
0,0
0,10,92
0,94
0,96
d2 I/
dV
2 (a.u
.) d
I/d
V (
G 0)
Energy (meV)
19K.S.Thygesen and K.W. Jacobsen (unpublished)
New local density calculations
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Vibration modes of a Pt – H2 – Pt bridge
0 20 40 60 80 100 1200
10
20
30
40
50 PtH2
C
ou
nt
Energy (meV)
21
PtD2
-100-80 -60 -40 -20 0 20 40 60 80 100-0,2
0,0
0,96
0,98 PtD2
d
2 I/dV
2 (a.
u.)
dI/d
V (
G0)
Energy (meV)
Vibration modes for Deuterium, Pt–D2–Pt
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-100 -80 -60 -40 -20 0 20 40 60 80 100
-0,1
0,0
0,1
0,98
1,00
1,02
1,04
same as stretched by 0.05 nm
d
2 I/dV
2 (a.
u)
d
I/dV
(G
0)
Energy (meV)
PtD2Vibration modes for Deuterium, Pt–D2–Pt
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PtD2
K.S.Thygesen and K.W. Jacobsen (unpublished)
-0,7 -0,6 -0,5 -0,4 -0,3 -0,2 -0,1 0,0
45
50
85
90PtD
2 stretching
En
erg
y (m
eV)
X (A)
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Comparison H2 and D2
0 20 40 60 80 100 1200
10
20
30
40
50 PtH2
Co
un
t
Energy (meV)
0 20 40 60 80 100 1200
10
20
30
40
50
60
70
PtD2
Co
un
t
Energy (meV)
25
Scaling of the modes by √m
20 40 60 80 100 120 1400
10
20
30
40
50
60
70 PtD
2
PtD2
PtD2
PtH2
PtH2
C
ou
nt
Energy (meV)
Ö2
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Scaling of the modes by √m
0 20 40 60 80 100 120 1400
10
20
30
40
50
60
70 PtD2
PtD2
PtD2
PtHD PtHD PtH
2
PtH2
C
ou
nt
Energy (meV)
Ö2
Ö3/2
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A test case for model calculations
J. Kuipers and M.C. van Hemert, unpublished
Conduction by antibonding orbitals. G = 0.9 G0.
N. Lang (Nature 419 (2002) 906) .
M.C. van Hemert, (Nature 419 (2002) 906)
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A test case for model calculations
Y. Garcia, J.J. Palacios, et al., cond-mat/0310098
Conduction by bonding orbitals. ΔE=23eV.G = 0.2 G0.
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A test case for model calculations
J. Heurich, F. Pauli, J.C. Cuevas, W. Wenzel and G. Schön, Nanotechnology 14
(2003) R29.
Conduction by bonding orbitals. ΔE = 24eV.
G = 0.86 G0
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A test case for model calculations
K. Thygesen and K.W. Jacobsen, unpublished.
Conduction by antibonding orbitals. ΔE = 10-13 eV.
G = 1.0 G0
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CO and Pt (preliminary)
0 1 2 3 4 5
10000
20000Pt-CO
Pt
Co
un
ts
Conductance (2e2/h)-50-40-30-20-10 0 10 20 30 40 50
-0,1
0,0
0,1
0,94
0,96
0,98
d2 I/d
V2 (
a.u
.)
d
I/dV
(2e
2 /h)
Energy (meV)
Pt-CO
-80 -60 -40 -20 0 20 40 60 80
-0,2
0,0
0,2
0,900,920,940,960,98
d2 I/d
V2 (
a.u
.)
d
I/dV
(2e
2 /h)
Energy (meV)
Pt-CO
-100 -50 0 50 100
-0,2
0,0
0,2
0,900,920,940,960,98
d2 I/d
V2 (
a.u
.)
d
I/dV
(2e
2 /h)
Energy (meV)
Pt-CO
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Conclusions
• Molecular hydrogen forms a nearly ideal conductor when placed between Pt electrodes, despite the closed-shell character of the free molecule.
• Single-molecule junctions can be characterized by the vibration modes, their stretching dependence, by the conductance and by the number of conduction channels.
• Hydrogen forms a good test-case for model calculations.
• More work on larger organic molecules …
Universiteit Leiden
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-100-80 -60 -40 -20 0 20 40 60 80 100
0,92
0,94
0,96
0,98
1,00
1,02
1,04Pt-D
2
Pt-HD (low)
G (
G0)
Energy (meV)
-100-80 -60 -40 -20 0 20 40 60 80 100
-0,2-0,10,00,10,2
0,94
0,96
0,98Pt-HD switching
d2 I/d
V2 (
a.u
.)
d
I/dV
(G
0)
Energy (meV)
Switching behavior for HD
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PtHD puzzle
-1,5 -1,0 -0,5 0,0
40
50
60
70
80
E
ner
gy
(meV
)
x (Å)
Switching during stretching