By Professor Geoff Ashwell
ESI Special Topics,
February 2003
Citing URL - http://www.esi-topics.com/fbp/2003/february03-GeoffAshwell.html
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Professor Geoff Ashwell answers a
few questions about this month's fast breaking paper in the field of
Materials Science.
From
•>>February 2003
Field: Materials Science
Article Title:
"Molecular rectification using a gold/(LB film)/gold structure"
Authors: Ashwell,
GJ;Gandolfo, DS
Journal: J MATER CHEM
Volume: 11
Page: 246-248
Year: 2001
* Cranfield Univ, Ctr Photon & Opt Engn, Nanomat Grp, Whittle Bldg, Cranfield MK43 0AL, Beds, England.
* Cranfield Univ, Ctr Photon & Opt Engn, Nanomat Grp, Cranfield MK43 0AL, Beds, England.
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 Why
do you think the paper is highly cited?
There has been a long-term interest in molecular electronics
and this was the first publication to report molecular
rectification for a Langmuir-Blodgett film of
donor-bridge-acceptor molecule sandwiched between gold
electrodes. All previous attempts to demonstrate the effect
concerned metal/(LB film)/metal structures where, to prevent
shorting through the fragile organic layer, the top electrode
was restricted to metals with low sublimation temperatures.
These readily oxidize and an unambiguous assignment of the
current-voltage characteristics to the organic film rather than
the oxide layer was not possible.
Does
it describe a new discovery or new methodology that’s useful to
others?
The paper probably describes both: it develops a method to
align polar molecules and provides the first successful
current-voltage characterization of a gold/(D-bridge-A)/gold
device, which demonstrates molecular rectification.
What
were the circumstances that led you to do this research?
There has been a long-term interest dating back to when my
group provided a zwitterionic dye to Professor Sambles at the
University of Exeter for a collaborative study on molecular
rectification (Phys. Rev. Lett. 70: 218, 1993). This
preliminary work showed promising data but using a silver-coated
magnesium top electrode rather than gold.
Could
you summarize the significance of your paper in layman’s terms?
The molecular rectifier is the organic counterpart
of the pn junction and comprises electron donating and accepting
groups linked via an electron bridge. If the molecules are
sandwiched as an organized film between metal electrodes,
gold/(D-bridge-A)/gold, electrons will tunnel under an appropriate
applied voltage from the electrode to acceptor at one end of the
device and from the donor to electrode at the other end. However,
when the bias is reversed, tunneling is not readily attainable
because the electron-donating end of the molecule is a poor
acceptor and the electron-accepting end is a poor donor.
Consequently, asymmetric current-voltage characteristics arise.
The molecular rectifier was first proposed three decades ago but
experimental verification has proven difficult. It requires an
ultra-thin organic layer to be sandwiched between non-oxidizable
electrodes and shorting frequently occurs during fabrication.
Significantly, the use of a gold/(D-bridge-A)/gold structure was
the first unambiguous assignment of asymmetric current-voltage
curves to molecular rectification.
Professor Geoff Ashwell
The Nanomaterials Group
Cranfield University
Cranfield, UK
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ESI Special Topics,
February 2003
Citing URL - http://www.esi-topics.com/fbp/2003/february03-GeoffAshwell.html
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