Introduction Sample preparation (1,4-benzenedimethanethiol (BDMT) )

1. 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

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

12. 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 1. grow self-assembled monolayers (SAMs) 2. compose circuit and drop solution aqueous solution of 0.1 M of K2PtCl4 and 0.5 M of H2SO4 pin hole A A SAMs 3. deposit Pt electrochemically 4. measure IV characteristics Pt this A Schematic diagram

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

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

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

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

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

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

24. 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.