Prof. Marika Schleberger’s research team has succeeded in collaboration with French researchers in creating the first regular chains of nanoscale “hillocks”, or nanodots, on an insulator surface. The dots are four nanometres high and evenly distributed less than 50 nanometres apart. This was possible by shooting ions with a kinetic energy of 92 MeV (megaelectronvolts) at grazing incidence onto the surface of a crystal. The ions were created at the GANIL accelerator in Caen, France.
The length of the chain, and thereby the number of nanodots, can be varied according to the angle of incidence. Each chain of dots is created by a single incident ion. No other method of producing this type of structure exists to date. Such nanostructures are interesting for a variety of applications, including the manufacture of biochips or modification of high-temperature superconductors.
The ions are so fast that they interact virtually only with the electrons of the crystal and not with the cores. Since the electrons are not distributed homogeneously in the material, energy transfer only occurs when the ion passes through a high-density area of the crystal. In other words, the observed dots are nothing other than a projection of the electron density, rendered visible by the grazing incidence.
To examine molecules relating to even smaller structures, the members of Prof. Rolf Möller’s research group have built their own scanning tunnelling microscope. The piezo-driven scanner operates at temperatures between 6 and 300 Kelvin, which makes it possible to freeze out molecular motion and examine organic systems with submolecular resolution. Current studies focus onthe organic molecule copper-phthalocyanineon a Cu(111) surface. The stability of the low-temperature scanning tunnelling microscope additionally allows local spectroscopy at surfaces and on single molecules. The researchers are particularly interested in this context in surfacereactions on the atomic and molecular scale.
Another important objective is to examine and understand the phenomena of friction and damping at surfaces. Experiments in this field use the measuring principle of atomic force microscopy. This method makes it possible to record not only topography but also energy losses at the surface.
Prof. Hans Werner Diehl’s research group has a completely different approach to nanosciences. What happens when two parallel, grounded metallic plates are in a vacuum? Surprisingly enough, they mutually attract. This force was discovered by Hendrik Casimir in 1948 and is of quantum-mechanical origin. It originates from the presence of fluctuating electromagnetic fields in a vacuum.
 In nanoelectromechanical systems (NEMS) Casimir forces can cause parts of NEMS to stick together, which restricts their function. There is consequently a great deal of interest in producing repulsive and controllably variable Casimir forces.
Similar fluctuation-induced forces can also be induced by thermal fluctuations in a substance that is at a critical point. Familiar examples are liquids at the end of the vapour pressure curve, where the difference between the liquid and gas phases disappears. These so-called thermodynamic Casimir forces are highly dependent on temperature and have been verified by experiments.
Prof. Hans Werner Diehl’s research group has carried out in-depth theoretical investigations into the critical Casimir force between parallel walls. It turns out that the Casimir amplitude, which is dependent on boundary conditions, in general must be replaced by a function that depends on the ratio between the wall separation and a wall-related length. Further, alternation between attractive and repulsive forces is possible. Since the wall-fluid interactions can be varied by careful selection of the liquid components and the wall materials, as well as by chemical modification of the walls, it should be possible to verify these predictions experimentally.
A further central topic for the researchers at the Faculty of Physics is improving modern electronics. Research in this field concerns the transport and control of carriers in semiconductors, where the information carriers are negative or positive charges. In future, electronics will not only use the charge but also the spin carried by every electron. If a current is sent through a ferromagnetic layer, the spins of the electrons are aligned and polarised. The spin-polarised current can be used in innovative components to store information at high density.
The physicists of Collaborative Research Centre SFB 491 in Bochum and Duisburg-Essen are growing innovative layer combinations using complex methods and under ultraclean conditions. They are concerned with the transport and manipulation of electron spins and the resulting new physical phenomena. Injection of spins also influences optical and superconducting properties.
The theoretical research work of Prof. Peter Kratzer’s research group deals with a similar topic. It is focused on thin-layer materials that will lend silicon-based electronics the functionality of magnetic materials. The researchers have calculated that very thin manganese-silicon layers can be magnetic at room temperature, even though common manganese and silicon alloys only exhibit magnetic behaviour after cooling. Implantinga single layer of manganese in silicon could also produce some interesting magnetic properties.
Domain walls play an important role in modern storage media on account of the diminishing size of domains and increasing storage densities. The research group under Prof. Peter Entel has been examining the influence of domain walls in cobalt-platinum layers on electrical resistance.