Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Communication in an Indirect Way

06.03.2013
Organic materials are comparatively poor conductors of electricity. Under certain conditions, however, this can change significantly. University of Würzburg physicists have now experimentally determined how exactly such a change in conductivity works in a two-dimensional layer.

Organic semiconductor materials have numerous advantages: They are inexpensive to synthesize in large quantities, easy to process, mechanically flexible and resource-efficient.


If a monolayer of organic molecules is deposited on a metal substrate, the conductivity of the organic material is significantly enhanced – as University of Würzburg physicists have just found out.
Graphics Peter Puschnig, Michael Wießner

However, their large-scale use in technological applications, such as optoelectronic components, is hampered by the fact that they generally conduct electric current rather poorly. But their conductivity can increase significantly in special conditions. Together with scientists from Graz and Hiroshima, University of Würzburg physicists have now clarified the reason why this is possible. Their research is reported in the current issue of the journal Nature Communications.

The experiment

"If organic molecules are deposited on a metal surface, the direct bond between these molecules is usually relatively weak," Achim Schöll explains. "The individual molecules mainly interact with their substrate instead." Schöll, a private lecturer at the Department for Experimental Physics VII of the University of Würzburg, has been spending many years of research on molecules that might be used in organic semiconductor electronics. In his latest experiments, he was able to show that the rule about the weak intermolecular interaction does not always apply.

For this purpose, the physicists deposited an ordered one-molecule-thick monolayer of organic molecules on a metal substrate in an ultrahigh vacuum. "Thus, we virtually created a two-dimensional semiconductor, in which the arrangement of the molecules is determined by the metal substrate," Schöll describes the method. When arranged in this way, the organic molecules exhibit quite unusual behavior.

The results

"We have verified that the electrons of the organic molecules now make contact with neighboring molecules – which process is mediated by the metal substrate," Schöll explains. In other words: The electron clouds of neighboring molecules assume a shared state, in which the metal is also involved. This facilitates the exchange of charge carriers, thus enhancing the conductivity of the organic material. What makes the results so fascinating is the fact that the molecules "communicate" with each other only indirectly by way of the metal substrate, as Schöll points out.

When conducting their measurements, the physicists came across another phenomenon as well: "The magnitude of this communication is highly direction-dependent," Schöll notes. This means that the two-dimensional layer of molecules is able to transfer charge carriers relatively easily in one specific direction whereas charge transport is significantly reduced in other directions. This is due to the internal structure of the molecules and their special arrangement on the metal substrate.
High degree of technological sophistication

The specimens used by the Würzburg physicists look like fingernail-sized metal disks. There is more to them than meets the eye, though, their preparation and examination involving a high degree of technological sophistication. In order to create layers of sufficient purity and order, for instance, you need a so-called ultrahigh vacuum, an extreme vacuum where the residual gas atoms are few and far between. In such a vacuum chamber, the pressure does not exceed 10 to the power of -10 millibar, which is below the pressure in near-earth space.

High tech equipment is also used to trace the behavior of the electrons in the specimen – the relevant method is called angle resolved photoelectron spectroscopy. An electron storage ring, i.e. a type of particle accelerator, producing so-called synchrotron radiation, serves as a source of UV radiation, which enables the researchers to take a look into the nanoworld.

The next steps

"This work is basic research in the field of nanoanalytics," says Schöll. For any future applications, however, it is essential to comprehend the complex interactions between organic molecules and the metal substrate. With their publication in Nature Communications, the researchers have by no means exhausted this topic. In further experiments, Schöll now intends to explore how a combination of various molecules, another substrate and a different arrangement of the molecules impact on the behavior of the electrons. The results from these experiments might be used to produce tailored two-dimensional networks with special electronic properties.

Substrate-mediated band-dispersion of adsorbate molecular states. M. Wießner, J. Ziroff, F. Forster, M. Arita, K. Shimada, P. Puschnig, A. Schöll & F. Reinert. Nature Communications, DOI: 10.1038/ncomms2522

Contact person
PD Dr. Achim Schöll, T: (0931) 31-85127, achim.schoell@physik.uni-wuerzburg.de

Gunnar Bartsch | Uni Würzburg
Further information:
http://www.uni-wuerzburg.de

More articles from Physics and Astronomy:

nachricht Computer model predicts how fracturing metallic glass releases energy at the atomic level
20.07.2018 | American Institute of Physics

nachricht What happens when we heat the atomic lattice of a magnet all of a sudden?
18.07.2018 | Forschungsverbund Berlin

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Future electronic components to be printed like newspapers

A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.

The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

A smart safe rechargeable zinc ion battery based on sol-gel transition electrolytes

20.07.2018 | Power and Electrical Engineering

Reversing cause and effect is no trouble for quantum computers

20.07.2018 | Information Technology

Princeton-UPenn research team finds physics treasure hidden in a wallpaper pattern

20.07.2018 | Materials Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>