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

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…

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

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

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

Organic Examples

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

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

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

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

DNA as an Electrical Conductor

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

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

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

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

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

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

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

Electrical Properties Length relationship Diameter relationship

Energy to Transmission Relationship

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

Possibilities ENDLESS!!!

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

Questions???