(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

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

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)

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

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

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

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

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.

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.

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

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

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.

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

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

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

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).

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 )

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.