Sustainability research

The Faculty of Physics began offering its Energy Science programme in 2011. The main motivation behind the concept was an observation that many professors have knowledge that they can contribute to creating sustainable energy supply. That is especially apparent in the case of Prof. Martina Schmid, who has succeeded in optimising the efficiency of solar cells. Prof. Michael Schreckenberg – a well-known traffic congestion researcher – is contributing through his research to reducing the number of vehicles senselessly causing pollution on the roads. Prof. Rossitza Pentcheva and Prof. Björn Sothmann are concerned with the conversion of heat into electrical energy. Prof. Michael Farle and Prof. Heiko Wende are helping to cut energy consumption by developing energy-optimised permanent magnets for electric motors and more efficient magnetocaloric materials for innovative refrigeration technologies. Prof. Axel Lorke is conducting research into carrier materials for electrochemical applications, such as catalysts and micro fuel cells, while energy-efficient IT systems are the goal of Prof. Claus Schneider’s work.

Thin film solar cells

The Schmid group focuses in its research on thin-layer chalcopyrite-based solar cells with the aim of achieving highly resource-efficient solar conversion. Here the researchers are exploring ultrathin solar cells with nanostructures on the one hand and developing micrometre-scale solar cells for light concentration on the other. A baseline for production of these solar cells was established during the reporting period and measuring systems for optoelectronic characterisation are available. Planning is already under way to expand the infrastructure to make way for further development in these areas.

Physics of transport and traffic

The Schreckenberg research group on Physics of Transport and Traffic is concerned with a variety of issues relating to the field of mobility research.

As part of CRC 876, the group is collaborating with electrical engineers to analyse inner-city traffic based on the example of Düsseldorf. Their aim is to cut congestion and travelling times without expanding road capacity. There are plans to extend simulation models to factor in the behaviour of automated vehicles so that hybrid traffic can also be simulated, analysed and optimised.

The MEC-View project, funded by the Federal Ministry for Economic Affairs and Energy (BMWi), is exploring automated driving in complex urban traffic scenarios, for example automatically entering a priority road. Its aim is to make urban traffic safer and more efficient. In collaboration with the project’s partners, the research group is developing theoretical traffic models based on real traffic data.

Thermoelectric energy harvesting on the nanoscale

The current energy crisis makes it necessary to explore and develop new sources of energy. One such possible source is thermoelectric energy harvesting, which converts thermal energy into electrical energy. Thermoelectric effects are especially strong in nanoscale systems, where quantum mechanical effects play an important role. Working with Peter Samuelsson from Lund University, members of the Sothmann research group have derived general boundaries for the power and efficiency of heat engines that work on the basis of quantum mechanical phase coherence. Thermoelectric effects are not only interesting on account of their potential applications, however, and can also have a role in characterising quantum states. In collaboration with Pablo Burset from Aalto University in Helsinki, for example, researchers were able to show that a finite Seebeck effect is a sure sign of supraconducting correlations that are nonlocal in time.

Nanoscale oxides for energy conversion

The diverse physical properties of transition metal oxides mean that they have many electronic, spintronic and energy conversion applications. For practical reasons, it is very important that they are ecological, stable and inexpensive. For ten years, the interfaces of transition metal oxides have been a focus of scientific inquiry, as it is here that new phenomena not found in the bulk occur and present new possibilities for targeted optimisation of functionality. The Pentcheva research group is interested in understanding and predicting the complex behaviour of such systems using large-scale quantum mechanical computer simulations based on density function theory.

Nanoscale magnetic systems

The Farle research group works on the static and dynamic properties of nanoscale magnetic systems. Synthesis and characterisation of new materials open up a range of applications, including energy-optimised permanent magnets for electric motors and magnetocaloric materials for innovative refrigeration technologies.

Another main interest of the Farle group is in the development of customised hybrid nanoparticles for medical theranostics. This combination of therapy and diagnosis presents new types of therapy to fight diseases such as cancer. Biocompatible magnetite-gold nanoparticles improve contrast in magnetic resonance imaging threefold compared to commercial contrast agents and can simultaneously be used during visualisation to transport drugs to the seat of disease. Cancer cells can additionally be targeted by thermal treatment, generated by magnetic alternating fields in the 300 kHz range.

Solid-state physics in different dimensions

The Lorke research group is concerned with structures that are limited in one or more spatial dimensions. Graphene is an example of such a system. It consists of only a single layer of carbon atoms, which means that the electrons within it can only move in two dimensions – in the third dimension they are “frozen” in the quantum mechanical ground state. This results in many unusual properties, which are interesting both for basic research and applications. For example, vertically aligned multiple layers of graphene – so-called carbon nanowalls – have potential as carrier materials for electrochemical applications, e.g. catalysts and micro fuel cells, on account of their large surface area . Research in this area is being conducted as part of a three-year project, MoreInnomat, funded by the European Union, with researchers from Chemistry, the hydrogen and fuel cell centre ZBT, and industrial partners.

Suppression of the Verwey transition in magnetite nanoparticles

Magnetite nanoparticles are utilised for both basic research and application purposes thanks to their interesting inherent properties. Magnetite is distinguished by a phase transition at 123 K (-150°C), the Verwey transition, where the physical properties, e.g., electrical conductivity, change abruptly.

It is difficult to characterise this phase transition in an ensemble of nanoparticles via diffraction methods. In cooperation between Dr. Carolin Schmitz-Antoniak (Forschungszentrum Jülich), members of Prof. Heiko Wende’s research group and theoreticians from Uppsala University (Sweden), the Verwey transition in nanoparticles was successfully analysed in detail using x-ray absorption spectroscopy at the BESSY-II synchrotron radiation source in Berlin.

New insight into redox reactions at interfaces

The Schneider research group is exploring the properties of new materials for information and energy technologies. One methodological focus of their work is on spectroscopy and spectromicroscopy with synchroton radiation at the BESSY (Berlin), PETRA (Hamburg) and Elettra (Trieste) sources. A main research interest is in spin electronics, i.e., spin-based phenomena. Diluted magnetic semiconductors play a central role in this area, as they combine the properties of semiconductors and magnets in a single material. Using hard x-ray photoemission spectroscopy, members of the research group have examined the bulk-electronic structure of GaMnAs and GaMnP in detail and for the first time separated the contributions made by the individual chemical components. This provides a basis for determining the cause of ferromagnetism in these materials, which is still a matter of some debate.