This phenomenon was previously only known from inorganic materials and is crucially important for future production of a new generation of semi-conductor components based on organic thin films. The data now published in the first July edition of SCIENCE was collated as part of a national research network funded by the Austrian Science Fund FWF.
Inorganic semi-conductors have a simple construction and have made high-performance computers possible. In contrast, organic semi-conductors are complex but enable production of innovative electronic circuits, as vividly demonstrated by the first prototypes for roll-up screens. Yet these benefits of organic semi-conductors can only be fully harnessed when the response of their organic molecular layer - whose thinness is crucial in functional terms - is better understood. The national research network (NRN) "Interface controlled and functionalised organic thin films" of the Austrian Science Fund FWF is contributing to precisely this understanding.
MICROSCOPIC HEIGHT MEASUREMENT
In the latest issue of SCIENCE, a team from the NRN has now been able to show that organic molecules spread out on a carrier material in a previously unknown form to create thin electrically conductive films. As Prof. Christian Teichert from the Institute of Physics at the University of Leoben explains: "Totally surprising diffusion behaviour at step edges formed during film growth was observed on the films of the organic substance parahexaphenyl produced by solid state physicists from Graz University of Technology. The molecules here come into contact with a diffusion barrier, which leads to the other molecules piling up. Although a diffusion barrier of this nature is well known in inorganic, atomically structured films it is called the Ehrlich-Schwoebel barrier in honour of its inventors - it had not previously been observed for organic materials."
The team in Leoben used scanning force microscopy to better understand this hitherto unknown behaviour of the organic molecules. This enabled precise measurement of the nano mounds at the step edges. Evaluation of the data thus obtained led to a further surprise. The shape of the nano elevations is strongly reminiscent of the terraced mounds encountered in mining. The team was struck by the fact that the terrace height of 2.6 nm almost exactly matches the length of a molecule of parahexaphenyl. The conclusion from this is that the molecules align themselves upright within a terrace.
However, it was also shown that the lower terraces are somewhat lower in height than those above. Project team member Dr. Gregor Hlawacek explains this phenomenon: "The data from the measurement allowed us to calculate the Ehrlich-Schwoebel barrier for this case. It also transpired that the molecules of the lower terraces are deposited at an angle. As a result, the terrace height here diminishes relative to the angle of inclination."
ENERGY-SAVING MEASURE AT NANO LEVEL
The measured values were used to perform computer simulations in the Chair of Atomistic Modelling and Design of Materials. These were not only able to confirm the experimental values for the diffusion barriers but also revealed that the parahexaphenyl molecules are bent in diffusion. This was surprising as bending requires expansion of the bonds in the molecule, which is in fact avoided owing to the energy required. However, in this way, the diffusing molecule can maintain bonds to neighbouring molecules more effectively than a rigid molecule, so that bending is overall the more energy-saving mechanism.
For the team from Leoben and Graz, these findings are extremely exciting as producing organic thin-film transistors requires closed films of such upright molecules. Improved understanding of the fundamental forces that bring this about will enable them to be manipulated and thus used in a controlled way. This NRN is therefore making a direct contribution to the future production of a new generation of semi-conductor components.
Image and text will be available online from Wednesday, 9th July 2008, 09.00 a.m. CET onwards: http://www.fwf.ac.at/en/public_relations/press/pv200807-en.html
Original publication: Characterization of Step-Edge Barriers in Organic Thin-Film Growth, G. Hlawacek, P. Puschnig, A. Winkler, C. Ambrosch-Draxl & C. Teichert. Science (2008), 108-111.
NASA spacecraft investigate clues in radiation belts
28.03.2017 | NASA/Goddard Space Flight Center
Researchers create artificial materials atom-by-atom
28.03.2017 | Aalto University
The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.
To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
29.03.2017 | Health and Medicine
29.03.2017 | Earth Sciences
29.03.2017 | Trade Fair News