Molecular Wires:Molecular Wires:The Next Generation of The Next Generation of

Electrical Devices?Electrical Devices?

Mike Van LinnMike Van Linn

Chemistry 496Chemistry 496

27 February 200427 February 2004

OutlineOutline

Down to nano-scaleDown to nano-scale

What are molecular wires?What are molecular wires?

The structureThe structure ““Wires”Wires” InsulationInsulation Connecting to electrical leadsConnecting to electrical leads

Physical theoriesPhysical theories

Electrical propertiesElectrical properties

Possible uses…Possible uses…

A Matter of ScaleA Matter of Scale

VERY SmallVERY Small

1 nm = 1x101 nm = 1x10-9-9 m m

10-10,000 atoms10-10,000 atoms

Changes in PropertiesChanges in Properties

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

NanoscienceNanoscience

-R. Tanke

Molecular WiresMolecular Wires

A molecule that connects two (or more) A molecule that connects two (or more) continuous electron reservoirs, or metallic continuous electron reservoirs, or metallic leadsleads

Organic compoundsOrganic compounds Usually highly conjugatedUsually highly conjugated

Organometallic compoundsOrganometallic compounds

Organic Examples Organic Examples

Synthesis of “Wires”Synthesis of “Wires”

PolymersPolymers LinearLinear

PAH’sPAH’s Conjugation (delocalization) importantConjugation (delocalization) important

Organometallic compoundsOrganometallic compounds

Electrical conduction is desiredElectrical conduction is desired

Insulating the WireInsulating the Wire

More efficientMore efficient

Use of cyclodextrin (a carbohydrate)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.

CyclodextrinCyclodextrin

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

Polyrotaxane “Stoppers”Polyrotaxane “Stoppers”

DNA as an Electrical ConductorDNA as an Electrical Conductor

Insulating the WireInsulating the Wire

More efficientMore efficient

Use of cyclodextrin (a carbohydrate)Use of cyclodextrin (a carbohydrate)

Protect from intermolecular interactionsProtect from intermolecular interactions AggregatesAggregates AtmosphereAtmosphere

Soluable in waterSoluable in water InkJet printersInkJet printers

Connecting to Electrical SourceConnecting to Electrical Source

Many problemsMany problems Connecting organic compound to metalConnecting organic compound to metal

Connecting to Electrical SourceConnecting to Electrical Source

Connecting to Electrical SourceConnecting to Electrical Source

Many problemsMany problems Connecting organic compound to metalConnecting organic compound to metal Formation of “tunnel junctions”Formation of “tunnel junctions”

Conduction barrier unless sufficient energyConduction barrier unless sufficient energy

Variable resistanceVariable resistance

Connecting to Electrical SourceConnecting to Electrical Source

Many problemsMany problems Connecting organic compound to metalConnecting organic compound to metal Formation of “tunnel junctions”Formation of “tunnel junctions”

Conduction barrier unless sufficient energyConduction barrier unless sufficient energy

Variable resistanceVariable resistance

DNA exampleDNA example Used carbon and rheniumUsed carbon and rhenium 20 KOhms over 0.5 20 KOhms over 0.5 µmµm

Physical TheoriesPhysical Theories

Landauer FormulaLandauer Formula

Lippmann-Schwinger’s EquationLippmann-Schwinger’s Equation

Schrodinger’s EquationSchrodinger’s Equation

Computational ApproxiamationsComputational Approxiamations Hartree-FockHartree-Fock HuckelHuckel

Landauer FormulaLandauer Formula

Lev Davidovich LandauLev Davidovich Landau Russian physicistRussian physicist Possible to calculate electronic conductionPossible to calculate electronic conduction

dG = dI w.r.t. VdG = dI w.r.t. V

Lippmann-Schwinger Eq.Lippmann-Schwinger Eq.

Gabriel Jonas LippmannGabriel Jonas Lippmann French physicistFrench physicist

Julian Seymour SchwingerJulian Seymour Schwinger American physicistAmerican physicist Worked with J.R. OppenheimerWorked with J.R. Oppenheimer

Used for analytical treatmentUsed for analytical treatment

Relationships between charged particles Relationships between charged particles in electric fieldsin electric fields

Electrical PropertiesElectrical Properties

Length relationshipLength relationship

Diameter relationshipDiameter relationship

Energy to Transmission RelationshipEnergy to Transmission Relationship

Energy to Transmission RelationshipEnergy to Transmission Relationship

The Future…The Future…

Molecular-sized Molecular-sized microchips, or microchips, or nanochipsnanochips

Transistors (a Transistors (a molecular switch)molecular switch)

Nanoscale electronic Nanoscale electronic devicesdevices Use of STM for Use of STM for

assemblyassembly Testing nanochipsTesting nanochips

PossibilitiesPossibilities

ENDLESS!!!ENDLESS!!!

ReferencesReferencesNitzan, Abraham and Michael Galperin; Nitzan, Abraham and Michael Galperin; Journal of Chemical PhysicsJournal of Chemical Physics, 2002, 117, 10837., 2002, 117, 10837.

Emberly, Eldon and George Kirczenow; Emberly, Eldon and George Kirczenow; NanotechnologyNanotechnology, 1999, 10, 285., 1999, 10, 285.

Dennis W. Bennett Inorganic Chemistry Laboratory for Surface Studies; “Molecular-Level Dennis W. Bennett Inorganic Chemistry Laboratory for Surface Studies; “Molecular-Level Wires,” Online posters.Wires,” Online posters.Link: Link: http://alchemy.chem.uwm.edu/research/bennett/posters/molwire/molwire.htmlhttp://alchemy.chem.uwm.edu/research/bennett/posters/molwire/molwire.html

Kalaugher, Liz; “Sugar coating insulates molecular wires,” Kalaugher, Liz; “Sugar coating insulates molecular wires,” Nanotechweb.orgNanotechweb.org, 23 Oct. 2002., 23 Oct. 2002.

Freemantle, Michael; Freemantle, Michael; Chemical and Engineering NewsChemical and Engineering News, 2002, 80, 17., 2002, 80, 17.

Ellenbogen, James C.; Ellenbogen, James C.; MITRE Nanosystems GroupMITRE Nanosystems Group, “A Fuctioning Molecular Wire,” 1996., “A Fuctioning Molecular Wire,” 1996.Link: Link: http://www.mitre.org/tech/nanotech/molecular_wire.htmlhttp://www.mitre.org/tech/nanotech/molecular_wire.html

““Conduction by molecular wires - the proof from DNA,” CNRS Info., March 2001.Conduction by molecular wires - the proof from DNA,” CNRS Info., March 2001.

Encarta Encyclopedia 2004.Encarta Encyclopedia 2004.

Questions???Questions???