Research
The basis for the thematic focus on nanoparticles and nanomaterials is formed by the internationally recognized collaborative research centre on “nanoparticles from the gas phase. Its object is the investigation of the processes whereby nanoparticles emerge from the gas phase – the opposite, say, of colloid chemical processes. The outcome has been important findings concerning the relationship between particle structure and particle properties which are indispensable for the use of nanomaterials in new applications such as new kinds of catalysts and new electrical or magnetic elements for sensors and solar cells. With its know-how on the production of nanoparticles of any defined diameter from a large number of materials, the Duisburg laboratory now enjoys a unique position worldwide.
Under the leadership of Prof. Christof Schulz from the Institute for Combustion and Gas Dynamics, three pilot plants have been set up at the Institute of Energy and Environmental Technology (IUTA) in Duisburg-Rheinhausen. These plants permit highly specific nanoparticles to be made available to industry in containers holding a few liters.
One interesting area of application for nanoparticles is nanobiomedicine. Matthias Epple, a professor of inorganic chemistry at Essen, is synthesizing DNA-functionalized inorganic nanoparticles on the basis of calcium phosphate for gene transfer purposes and for the production of bioactive surfaces. And nanocapsules – these are hollow nanoparticles – are being made by Prof. Christian Mayer from the Department of Physical Chemistry. It is hoped that of these capsules, when injected with the appropriate medicine, can be guided to the right part of the body before releasing their contents. In this way, locally effective treatment possibilities with minimal side effects can be developed.
The thematic focal point of nano-optoelectronics is represented by the research training group (Graduiertenkolleg) set up by the German Research Foundation DFG in 2006: “Nanotronics – Optoelectronics and Photovoltaics Made of Nanoparticles. The research training group draws on expertise in the field of nanoparticles, working with the vision of nanoparticles for the large-area and low-cost transformation of electrical energy into light and, vice versa, light into electrical energy. As such, the research training group is a cooperative venture with the Science-to-Business Centre Nanotronics Unit at the EVONIK/Degussa Company in Marl and is aiming to have trained eight specially qualified scholarship holders by the end of 2010. In Germany as a whole, there is only one other research training group funded by the German Research Foundation and working in partnership with an industrial company.
Dr. Cedrik Meier, a physicist, has succeeded in winning a next-generation competition organized by the German Federal Ministry of Education & Research and endowed with a prize of 1.5 million. What he did was to merge two highly topical research topics: photonic crystals and the material zinc oxide. Photonic crystals can be used to control the propagation of light via the material properties. For example, on a semi-conductor chip and in the smallest of spaces, light can be guided, decelerated or even locked in. Which means that the interaction between light and the semi-conductor can be boosted considerably, permitting the construction of new kinds of devices. The most important example of this are nanolasers which, working with a negligible laser threshold and acting as single photon sources, could play a major role in the realm of quantum information technology. Dr. Meier was elected by the North Rhine-Westphalian Academy of Science to its Junior Chamber.
The work of Dr. Nils Hartmann, from the Department of Chemistry, is connected thematically here – although completely different techniques are employed. He has succeeded in “building a one-dimensional chain of gold clusters with a 14 nm diameter. In the future, such structures could serve as light guides in computer chips, the advantage being that the information is transferred more swiftly than present electrical connections allow. The remarkable thing is this: in the preparation, Dr. Hartmann used very simple techniques – such as chemistry in beakers and writing on a substrate with a focused laser beam – in a configuration that all fits onto a laboratory bench.
This kind of light guide belongs to the new scientific field of plasmonics, which is also the field of Dr. Frank Meyer zu Heringsdorf. The latter has made the propagation of the plasmons in silver nanostructures visible with the aid of an electron microscope operating with exposure times of just ten femtoseconds (10-15 s).
At the other end of the technical input spectrum, in a newly-erected clean room specially set up for this purpose in the electrical engineering department, we find individual quantum points made of cadmium selenide being prepared. These are small crystals measuring 10 nm that can be deposited epitactically on gallium arsenide. These structures get their name from the fact that the crystals are not extended in any spatial dimension – i.e. they are (almost) punctiform – and as a result display evidence-based properties in quantum physics, in particular. Prof. Gerd Bacher and Dr. Tilmar Kümmell were the first to demonstrate the emission of green light from a single quantum dot at room temperature. Before this, light emission had only been achieved using cooled devices made up of millions of quantum dots.
Researchers at our Centre for Semiconductor and Optoelectronics (ZHO) have been able to demonstrate nanowire field-effect transistors with a diameter of only a few nanometers displaying an amplification twice as high as that achieved with any previously known field effect transistors.
For the research on nanomagnetism a central role is played by the collaborative research centre for “magnetic heterolayers – set up in collaboration with the Ruhr-Universität Bochum – and in addition MAGLOMAT, granted to Dr. Andreas Ney by the EU within the Marie Curie excellence programme. This deals with materials which in future may use the spin of the electron as a carrier of information in the world of electronics (aka “spintronics). The focal point of this research is the understanding of how magnetic order in a semiconductor comes about. To achieve this, magnetic nanoparticles are used as a model system in a semiconductor. In this context, silicate-encapsulated cobalt nanoparticles with diameters of between 20 and 30 nm are produced. Dr. Marina Spasova observed here that, in the course of this synthesis, self-organized structures with chain-and-ring-type formations would emerge if weak magnetic fields were applied during the synthesis. The cause is the magnetic dipole-dipole interaction; thanks to this uncomplicated method, pearl-chain-like structures can be generated. Molecular dynamic simulations like these carried out by Prof. Peter Entel, in which the dipolar magnetic forces are taken into account, permit a faithful reproduction of the self-organized structures.
The research programme in general also includes an examination of elementary processes. For example, via stroboscopic lighting using extremely short electron pulses, the researchers are in a position to follow the movement of atoms on surfaces – and thus take a closer look at melting processes and thermal conduction with a time resolution of femtoseconds (10-15 s).
The nanosciences can operate successfully only in the interplay between experiments and computer simulation. A major focus of theoretical research is the search for (1) materials with optimized magnetic and optical properties for applications in nanotechnology and spintronics as well as (2) for thin layer materials. This will, hopefully, allow silicone-based electronics to be extended by the functionality of magnetic materials. In this respect, Prof. Peter Kratzer has found that ultra-thin manganese silicone layers exhibit unusual magnetic behavior and have the potential to combine magneto-electronics with conventional electronics.
Finally, if we are to assume our social responsibility, it is essential that we also look at the ramifications of possible damage to cells and , i. e, the damage that may occur if nanoparticles get into the environment and are taken up by living organisms. For this reason, the University of Duisburg-Essen initiated a German Research Foundation priority programme under the leadership of Prof. Reinhard Zellner. The programme will be also coordinated by Prof. Zellner during the next few years.
