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Up & down
Organic semiconductors are manufactured by applying thin films of an
electrically conductive organic material to a carrier surface. When
carrying out this process, it is important to understand the
interactions that occur at the interfaces between the carrier material
and the organic material. A team from the "Interface controlled and
functionalised organic thin films".
National Research Network (NRN) at the University of Leoben has made
an important contribution to scientific understanding in precisely
this field.
Using complex calculations, the team has been able to show that a thin
film of organic thiophene is held on to a copper surface solely by the
van der Waals force. The team calculated that the adsorption energy
involved is -0.50 eV.
The spokesperson for the NRN, Prof. Helmut Sitter from the Institute
of Semiconductor and Solid State Physics at Johannes Kepler University
(JKU) in Linz, explains: "The van der Waals force is a weakly
interacting force between atoms that occurs as a result of asymmetric
charge distribution in atoms. We now know that this exerts a highly
significant influence on the kinds of extremely thin material films
used to manufacture organic semiconductors. Indeed, this force can
successfully bind the materials entirely on its own. However, due to
its weakness, several previous methods used to calculate the
interactions between different materials have attached only minor
importance to this force, or have ignored it altogether." This would
also seem to provide some explanation for why the generalized gradient
approximation (GGA) often used in such instances has been unable to
satisfactorily explain the bonding behaviour in thin layers. In fact,
these newly published results could explain the discrepancies that
have long been found between various experimental data and models for
calculating the interaction between thin layers.
Publications, prizes, products
The new data adds to our fundamental understanding of the interactions
that take place at interfaces. The influence of the van der Waals
force also indicates that no charge is transferred between the atoms
of the organic materials and their substrates in the calculated
system. This finding is of key significance to the production and
functionality of organic semiconductors.
Several articles in the Advanced Materials journal this year
demonstrate how research carried out by members of the NRN maintains a
steady focus on practical applications. As a result of one such
article, the Institute of Experimental Physics at JKU won the official
Innovation Prize of the Province of Upper Austria. It is no surprise
that three spin-off companies � run almost exclusively by graduates
from the Institutes involved in the NRN � have already been
established as a direct result of the findings. One of these companies,
Nanoident, was declared "Entrepreneur of the Year 2007" by Ernst &
Young Austria.
Prof. Sitter believes that all of these achievements, together with an
article by the NRN published in SCIENCE in the summer of this year,
prove how this National Research Network has successfully combined
fundamental research, applied research and technology transfer � with
the support of the FWF.
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