1. (Applied Physics Letters, 2004 (in press))
Temperature Dependent Molecular Conduction measured by the Electrochemical Deposition of Platinum Electrode in Lateral Configuration
(Applied Physics Letters, 2004 (in press))
B. Kim*, S. J. Ahn*, J. G. Park*, S. H. Lee*, E. E. B. Campbell**, Y. W. Park*
* School of Physics, Seoul National University, Korea
** Department of Experimental Physics, Gothenburg University and Chalmers University of Technology, Sweden

2. Introduction
Sample preparation
(1,4-benzenedimethanethiol (BDMT) )
III. Result and discussion: Temperature dependent molecular conduction (27K<T<300K) in lateral configuration
IV. Summary

3. Polyacetylene single nanofiber(PANF)
Poster 24: Bio Kim et al.
0.8 micron
AFM image
SEM image
Synthetic Metals 119, 53 (2001)

4. Scanning tunneling microscope
S. Datta, et al., Phys. Rev. Lett. 79, 2530 (1997)
M. Dorogi, et al., Phys. Rev. B, 52, 9071 (1995)

5. Conducting atomic force microscope
X. D. Cui, et al., Science, 294, 571 (2001)
D. J. Wold, et al., J. Am. Chem. Soc. 123, 5549 (2001)

6. Mechanically controlled break junction
J. Reichert, et al., Phys. Rev. Lett. 88, (2002)
M. A. Reed, et al., Science, 278, 252 (1997)

7. Electromigration break junction
J. Park, et al., Nature 417, 722 (2002)
H. Park, et al., Appl. Phys. Lett. 75, 301 (1999)

8. Angle evaporation
N. B. Zhitenev, et al., Phys. Rev. Lett. 88, (2002)
J. O. Lee, et al., Nano Lett. 3, 113 (2003)

9. Others J. G. Kushmerick, et al., Nano Lett. 3, 897 (2003)
J. K. N. Mbindyo, et al., J. Am. Chem. Soc. 124, 4020 (2002)

10. Molecular conduction measured by the electromigration technique
2. Electrode design
1. Electromigration
200 nm
2 ㎛
20 nm height of Au electrode without adhesion layer
H. Park, et al., Nature 407, 57 (2000)

11. 3. Breaking of Au line
4. AFM and SEM image of nano gap

12. Molecular conduction measured by the electrochemical deposition
Our method:
Molecular conduction measured by the electrochemical deposition
(1) SAM on top of Au
electrode/nanoparticles
David L. Klein et al., APL 68, 2574 (1996)
(2) reducing the separation of
electrodes using electrochemical
deposition of Pt
Y. V. Kervennic, et al., Appl. Phys. Lett. 80, 321 (2002)

13. Our method: (1) + (2)
combination of electrochemical deposition and SAM
Schematic diagram
1. grow self-assembled monolayers (SAMs)
SAMs
pin hole
2. compose circuit and drop solution A
aqueous solution of 0.1 M of K2PtCl4 and 0.5 M of H2SO4 A
3. deposit Pt electrochemically Pt
4. measure IV characteristics A
this

14. Electrochemical deposition process of Pt
In the electrolyte
In situ
In the electrolyte
In the electrolyte
time
R > 10 G
Optical microscope image confirms the deposition of Pt on one side.
After drying electrolyte

15. AFM & FESEM image before deposition after deposition height ~ 700 nmPt Pt
100 nm
height ~ 700 nm Pt
SiO2
side view (conjecture)

16. Measurement results & discussion
At Room Temperature
open
R > 10 G
short
R ~ 5 k
sample
non-Ohmic

17. Temperature dependent I-V characteristics (160K<T<300K)
sample 1
Temperature dependent I-V characteristics (160K<T<300K)
The I-V characteristics are non-Ohmic and asymmetric in all temperature range, and current decreases upon cooling (semiconductor- like temperature dependence) .
The asymmetric
characteristics are originated by the difference of the two contacts: one Pt electrode is chemisorbed and the other Pt electrode is physisorbed.to the molecule.

18. Temperature dependent I-V characteristics (29K<T<120K)
sample 1
Temperature dependent I-V characteristics (29K<T<120K)
There is no significant temperature dependence in the I- V characteristics below 40 K. This means that the tunneling conduction is dominant at T< 40K.

19. Tunneling at low temperature (T<40K)
sample 1
Tunneling at low temperature (T<40K)
Fowler-Nordheim tunneling:
log(I /V2) ∝ -1/V

20. Temperature dependent I-V characteristics (100K<T<300K)
sample 2
Temperature dependent I-V characteristics (100K<T<300K)

21. Temperature dependent I-V characteristics (27K<T<100K)
sample 2
Temperature dependent I-V characteristics (27K<T<100K)
I-V curves show very stable behavior below 0.85 V, but the current fluctuates for V> 0.85 V at 50 K < T < 60 K.

22. I-V characteristics – sample 2
No switching or NDR effect upon voltage sweep at T=27K
At T=27K
At T=27K
After sweeping the voltage,
the current is increased ~5 times

23. I-V characteristics (30K<T<100K)
sample 2
I-V characteristics (30K<T<100K)
And the RTS-like fluctuation at
50 K < T < 60 K
is disappeared

24. Tunneling at low temperature (T<40K)
sample 2
Tunneling at low temperature (T<40K)
Fowler-Nordheim Tunneling:
log(I /V2) ∝ -1/V

25. Model for the asymmetric I-V characteristics
positive bias to ‘physisorbed Pt’
LUMO eV
Chemisorbed Pt
Physisorbed Pt
negative bias to ‘physisorbed Pt’
HOMO eV
Contact between base Pt and SAM is much better (chemisorbed) than contact between electrochemically grown Pt and SAM (physisorbed).

26. Summary · Temperature dependent molecular conduction was
measured by the electrochemical deposition of platinum
electrode to the self-assembled monolayer of
1,4-benzenedimethanethiol (BDMT) in lateral configuration.
· I-V characteristics are non-Ohmic and asymmetric in all
measured temperature range. (27 K < T < 300 K)
· For T>40K, the I-V characteristics are semiconductor-like.
· For T40K, the I-V characteristics are temperature
independent following the Fowler-Nordheim type
Tunneling conduction. ( log (I /V2) ∝ -1/V )

27. Acknowledgement:
This work was supported by the National Research Laboratory (NRL) program of the Ministry of Science and Technology (MOST), Korea.
Work done in Sweden was supported by the Sweden Strategic Research Fund (CARAMEL consortium) and STINT.
Partial support for Yung Woo Park was provided by the Royal Swedish Academy of Science.