1. Molecular Wires: The Next Generation of Electrical Devices? Mike Van Linn Chemistry 496 27 February 2004

2. Outline Down to nano-scale What are molecular wires? The structure “Wires” “Wires” Insulation Insulation Connecting to electrical leads Connecting to electrical leads Physical theories Electrical properties Possible uses…

3. A Matter of Scale VERY Small 1 nm = 1x10 -9 m 10-10,000 atoms Changes in Properties

4. Nanoscience is defined as the creation of useful/functional materials, devices and/or systems through control of matter on the nanometer scale and exploiting the properties at the macro-scale. Nanoscience -R. Tanke

5. Molecular Wires A molecule that connects two (or more) continuous electron reservoirs, or metallic leads Organic compounds Usually highly conjugated Usually highly conjugated Organometallic compounds

6. Organic Examples

7. Synthesis of “Wires” Polymers Linear LinearPAH’s Conjugation (delocalization) important Conjugation (delocalization) important Organometallic compounds Electrical conduction is desired

8. Insulating the Wire More efficient Use of cyclodextrin (a carbohydrate)

9. Cyclodextrin used to insulate the molecular wire. Used to produce green and blue LEDs. Helps prevent “red shift” from molecular interactions. Cyclodextrin

10. POLYROTAXANE Stoppers at both ends of conjugated polymer chain prevent unthreading from cyclodextrin rings. Polyrotaxane “Stoppers”

11. DNA as an Electrical Conductor

12. Insulating the Wire More efficient Use of cyclodextrin (a carbohydrate) Protect from intermolecular interactions Aggregates Aggregates Atmosphere Atmosphere Soluable in water InkJet printers InkJet printers

13. Connecting to Electrical Source Many problems Connecting organic compound to metal Connecting organic compound to metal

14. Connecting to Electrical Source

15. Many problems Connecting organic compound to metal Connecting organic compound to metal Formation of “tunnel junctions” Formation of “tunnel junctions” Conduction barrier unless sufficient energy Variable resistance

16. Connecting to Electrical Source Many problems Connecting organic compound to metal Connecting organic compound to metal Formation of “tunnel junctions” Formation of “tunnel junctions” Conduction barrier unless sufficient energy Variable resistance DNA example Used carbon and rhenium Used carbon and rhenium 20 KOhms over 0.5 µm 20 KOhms over 0.5 µm

17. Physical Theories Landauer Formula Lippmann-Schwinger’s Equation Schrodinger’s Equation Computational Approxiamations Computational Approxiamations Hartree-Fock Hartree-Fock Huckel Huckel

18. Landauer Formula Lev Davidovich Landau Russian physicist Russian physicist Possible to calculate electronic conduction Possible to calculate electronic conduction dG = dI w.r.t. V

19. Lippmann-Schwinger Eq. Gabriel Jonas Lippmann French physicist French physicist Julian Seymour Schwinger American physicist American physicist Worked with J.R. Oppenheimer Worked with J.R. Oppenheimer Used for analytical treatment Relationships between charged particles in electric fields

21. Electrical Properties Length relationship Diameter relationship

22. Energy to Transmission Relationship

24. The Future… Molecular-sized microchips, or nanochips Transistors (a molecular switch) Transistors (a molecular switch) Nanoscale electronic devices Use of STM for assembly Use of STM for assembly Testing nanochips Testing nanochips

25. Possibilities ENDLESS!!!

26. References Nitzan, Abraham and Michael Galperin; Journal of Chemical Physics, 2002, 117, 10837. Emberly, Eldon and George Kirczenow; Nanotechnology, 1999, 10, 285. Dennis W. Bennett Inorganic Chemistry Laboratory for Surface Studies; “Molecular-Level Wires,” Online posters. Link: http://alchemy.chem.uwm.edu/research/bennett/posters/molwire/molwire.html http://alchemy.chem.uwm.edu/research/bennett/posters/molwire/molwire.html Kalaugher, Liz; “Sugar coating insulates molecular wires,” Nanotechweb.org, 23 Oct. 2002. Freemantle, Michael; Chemical and Engineering News, 2002, 80, 17. Ellenbogen, James C.; MITRE Nanosystems Group, “A Fuctioning Molecular Wire,” 1996. Link: http://www.mitre.org/tech/nanotech/molecular_wire.html http://www.mitre.org/tech/nanotech/molecular_wire.html “Conduction by molecular wires - the proof from DNA,” CNRS Info., March 2001. Encarta Encyclopedia 2004.

27. Questions???