Transcript Molecular Wires

Molecular Wires:
The Next Generation of
Electrical Devices?
Mike Van Linn
Chemistry 496
27 February 2004
Outline
Down to nano-scale
What are molecular wires?
The structure
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
“Wires”
Insulation
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
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.
-R. Tanke
Molecular Wires
A molecule that connects two (or more)
continuous electron reservoirs, or metallic
leads
Organic compounds

Usually highly conjugated
Organometallic compounds
Organic Examples
Synthesis of “Wires”
Polymers

Linear
PAH’s
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Conjugation (delocalization) important
Organometallic compounds
Electrical conduction is desired
Insulating the Wire
More efficient
Use of cyclodextrin (a carbohydrate)
Cyclodextrin
Cyclodextrin used to insulate the molecular wire.
Used to produce green and blue LEDs.
Helps prevent “red shift” from molecular
interactions.
Polyrotaxane “Stoppers”
POLYROTAXANE Stoppers at both ends of conjugated
polymer chain prevent unthreading from cyclodextrin
rings.
DNA as an Electrical Conductor
Insulating the Wire
More efficient
Use of cyclodextrin (a carbohydrate)
Protect from intermolecular interactions


Aggregates
Atmosphere
Soluable in water

InkJet printers
Connecting to Electrical Source
Many problems

Connecting organic compound to metal
Connecting to Electrical Source
Connecting to Electrical Source
Many problems


Connecting organic compound to metal
Formation of “tunnel junctions”
Conduction barrier unless sufficient energy
Variable resistance
Connecting to Electrical Source
Many problems


Connecting organic compound to metal
Formation of “tunnel junctions”
Conduction barrier unless sufficient energy
Variable resistance
DNA example
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Used carbon and rhenium
20 KOhms over 0.5 µm
Physical Theories
Landauer Formula
Lippmann-Schwinger’s Equation
Schrodinger’s Equation
Computational Approxiamations
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Hartree-Fock
Huckel
Landauer Formula
Lev Davidovich Landau
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Russian physicist
Possible to calculate electronic conduction
dG = dI w.r.t. V
Lippmann-Schwinger Eq.
Gabriel Jonas Lippmann

French physicist
Julian Seymour Schwinger
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American physicist
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
Energy to Transmission Relationship
The Future…
Molecular-sized
microchips, or
nanochips
Transistors (a
molecular switch)
Nanoscale electronic
devices

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Use of STM for
assembly
Testing nanochips
Possibilities
ENDLESS!!!
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
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
“Conduction by molecular wires - the proof from DNA,” CNRS Info., March 2001.
Encarta Encyclopedia 2004.
Questions???