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Interfacing Molecules to Electronic Materials

Interfacing Molecules to Electronic Materials. Stuart.Lindsay@ASU.EDU. Artificial Enzymes Hydrogen generation, photovoltaics. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. Steinberg-Yfrach et al. Nature 392, 479 (1998).

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Interfacing Molecules to Electronic Materials

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  1. Interfacing Molecules to Electronic Materials Stuart.Lindsay@ASU.EDU

  2. Artificial Enzymes Hydrogen generation, photovoltaics + + + + + + + + + + + + + + + Steinberg-Yfrach et al. Nature 392, 479 (1998)

  3. 3. Make them function on electrodes like they do in solution 4. Make economically-viable devices Steps to bio/molecular electronics: 1. Make functional molecules 2. Wire molecules to electrodes

  4. -2e- Conductor -2e- Insulator Test Case: Single Molecule Switchmade from Oligo Aniline Insulator i V Single Molecule Switch?

  5. Molecular electronics vs. solution charge transfer chemistry • Charge transfer in nature in solution + ions. • Charge transfer in molecular electronics electrode to electrode – No water/ions

  6. e- Why solvent + ions matter LANDAUER 1 2 ENERGY e- LUMO CHARGED HOMO MARCUS

  7. Charge Transfer in DNA Barnett et al., Science 294 567 (2001)

  8. The Challenge Need to measure single molecule conductance in a conducting solution with independent control of charge state. How to do this?

  9. Repeated break junction Xu and Tao, Science 301, 1221-1223 (2003)

  10. Wiring Single Molecules Reliably GOOD NEWS:7000:1 G range – worst Gtheor/Gmeas is 3.3 BAD NEWS: All Landauer theory Cui et al. Science 274 571 (2001) Xu and Tao, Science 301 1221 (2003)

  11. Operating probes in electrolyte Insulating layer Rev. Sci. Instrum. 60, 3128 - 3130 (1989) (DNA - Xu et al. Nanoletts 4 1105 2004)

  12. Controlling ion gradients/electric fields at an electrode surface Bigger ion gradient = Bigger electric field at molecule

  13. Measuring transport as a function of oxidation state LOCAL FIELD SURFACE FIELD

  14. G=GMAX- a(ES-b)2 Molecular Conductance (nS) Electrochemical Current Surface Potential, ES , Vvs. Ag Ofer et al. JACS 112 7869, 1990 TIP-SUBSTRATE V FIXED AT 50mV Insulator Conductor Insulator

  15. (H2SO4) Oxidized molecule ES=0.4V FIX ES, VARY TIP FIELD Current (nA) (NO IONS) Neutral molecule - - - - - - Tip-substrate bias (V)

  16. =1.4 ES=0.3V ES=0.25V MOLECULE FIELD = SURFACE FIELD ± TIP FIELD G=Gmax-a(ES-b)2 ES(V) =ES-V Current (nA) - - - - - - Tip-substrate bias (V)

  17. We have a two terminal switch!

  18. But it will need more than one molecule: Bias sweeps Potential sweeps Current (nA) - - - Vts(Volts) ES(V vs. Ag Wire)

  19. Roadmap for going from chemistry to molecular electronics Summary • Made a low-voltage switch based on chemical knowledge, get NDR • Probe role of fluctuations

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