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Single Molecule Electronics And Nano-Fabrication of Molecular Electronic Systems

Single Molecule Electronics And Nano-Fabrication of Molecular Electronic Systems. S.Rajagopal , J.M.Yarrison-Rice Physics Department, Miami University Center For Nanotechnology, Oxford, OH. Highlights. Organometallic paddlewheel complex Fabrication of two electrode and gated

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Single Molecule Electronics And Nano-Fabrication of Molecular Electronic Systems

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  1. Single Molecule Electronics And Nano-Fabrication of Molecular Electronic Systems S.Rajagopal, J.M.Yarrison-Rice Physics Department, Miami University Center For Nanotechnology, Oxford, OH.

  2. Highlights • Organometallic paddlewheel complex • Fabrication of two electrode and gated devices using EBL • Closing of gap using electrodeposition • Breaking a nanowire by electromigration • Characterization of the fabricated nanogap

  3. Process Steps Fabricate nano-gap electrodes with EBL Close gap to nano-gap using electrodeposition Characterize the nano-gap Deposit molecule and study the gap

  4. Os-Os Triple bond • Ir-Ir Double bond The Molecule • Re-Re Quadruple bond • Paddlewheel bridging ligands • Anchoring thiol group

  5. Fabrication of Nanogap Electrodes C A B 300nm 300nm D E • Raith 150 EBL system • Different gold thickness (100/150/250 nm) on top of 30nm Cr

  6. Fabrication Results • Two electrode devices 1 • After EBL & development 2 • GDS2 design • Design gap 75nm • Gap=74nm 3 • After metal evaporation of Cr/Au • Gap=53nm

  7. Fabrication Results • Gated electrode devices 1 • GDS2 gated design • Design gap 60nm 2 • After metal evaporation of Cr/Au • Gap=10nm 3 • Gated device with 3 contact pads

  8. Closing the Gap Using Electrodeposition • Packaging = Wire bonding + Epoxy cavity 1 2 • Package: Kovar material • Wire bonding of contact pads to external leads ; Substrate temp ~150° C • Epoxy cavity for forming the electrochemical cell

  9. Factors To Consider • Method  Setup ( 2 methods tried ) • Electrolyte composition ( 2 compositions ) • Deposition current • Electrolyte concentration ( 4 concentrations)

  10. Closing the Gap Using Electrodeposition • Electrodeposition Setup 1 (Non Cyanide) • Method: Constant current ; Monitor the voltage across WE and RE • Electrolyte composition: 0.42 M Na2SO3 + 0.42 M Na2S2O3 + 0.05 M NaAuCl4 • Non-toxic and without strongly adsorbed ions • At room temperature

  11. Results of Electrodeposition (Method 1) • Time evolution curve of Vgap at a constant current of 25 µA on a chart recorder Stop • SEM image of fused electrodes after electrodeposition • I-V curve showing hysteresis

  12. Difficulties with Method 1 • Method requires precise switching on desired gap voltage  Manual ( less precise) • Open loop system (no feedback) • Lacks control on deposition rate • Solution stability problem • No two fabricated pairs showed the same growth pattern with similar initial/final gap voltages

  13. I tunnel I dep I total Faraday Cage I total = I dep + I tunnel Galvanostat 200μ WE DMM RE/CE Modified Setup – Self-terminating • Method: Constant current ; More directional growth • Preset current for desired gap : 5/10/20/50nA • Mix C & D : 0.4 M Na2SO3 + 0.4 M Na2S2O3 + 0.01 M Na2Au(S2O3)2 + 0.3 M Sodium citrate • Solution more stable (for more than 2 weeks) J. Xiang, B.Liu, B.Liu, B. Ren, Z.Q. Tian, Electrochemical Communications vol. 8, pp. 577-580, 2006

  14. Electrodeposition Results Mag=2.2 Kx I=-10nA Mag=36 Kx I=-10nA Left electrode Right electrode Mag= 15 Kx I=-10nA Left electrode Right electrode Abnormal growth But, fine grain size

  15. Results & Difficulties I (A) V (V) • Growth moderately fine, but not predictable in all pairs • Abnormal growth due to surface contamination • Small structural shapes of electrode not retained • Initial/Final V of nanogap showed no trend • All final I/V curves showed huge gaps

  16. Previous Revamped 700nm Design and Setup Changed • New design tried to retain shape and avoid folding patterns • New electrolyte delivery to localize to single pair • Solution modification to minimize deposits on other electrode • Minimize surface contamination

  17. Results – SEM Micrographs • Out of 8 pairs, 6 pairs showed similarly growth • A small gap (~10nm) could be realized using SEM images • Abnormal growth seems controlled • Electrode shape retained

  18. I-V Results of Nanogap Pair 1 Pair 2

  19. Steps Ahead • Design change 2 (Should make growth pattern more clear) • Investigate why no similarity in the I-V curve • Investigate affect of thickness of insulation layer on electrodeposition results (Use thicker insulation layer above substrate) • Effective way of depositing a long (~1nm) organic molecule across nanogap • Measure electrical characteristics after depositing the molecule

  20. Conclusion Molecule Land • Paddlewheel complex synthesized. • Anchoring ligands are attached. • Final analysis of the complex… Device Fabrication Land • Two electrode and Gated electrode device with larger nano-gap separation fabricated. • Electrodeposition parameters determined for achieving 10nm gap. • Fine-tuning of electrodeposition parameters for <10nm gap…

  21. Thank you !

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