Physics

Since particles with a diameter of very few nanometres have a high surface-to-volume ratio, they make it possible to examine the properties of materials between bulk and atomic or molecular structures. The focus of research in Prof. Heiko Wende’s team is on the magnetic properties of nanoparticles consisting of pure metals, metal oxides and ferromagnetic alloys. Magnetic dichroism in x-rayabsorption allows element-specific determination of the magnetic moments and separation of the orbital and spin moments. X-ray absorption spectroscopy also permits analysis of structure and local chemical composition. For example, in the past it was shown that the distribution of iron and platinum atoms in nanoparticles of an iron-platinum (Fe-Pt) alloy is inhomogeneous. This is associated with a reduction in the magnetic moments compared to the corresponding bulk material. An extreme example of such inhomogeneity in binary systems, core / shell particles, is an interesting topic for the future: these particles are composed of a core containing only one chemical element and a shell made of a different element. This not only protects the core from oxidation and other effects of aging, but may also facilitate bio-functionalisation for medical applications.
Silicon nanowires offer enormous potential in the manufacture of semiconductor components. Examples of possible future applications include nanometric transistors and ultra-efficient solar cells.
Often, the sidewalls of these nanowires are not smooth but exhibit a characteristic zigzag pattern (faceting). For a long time, there was speculation as to whether gold causes the facets to form. “Gold is used as a catalyst to grow the wires and could diffuse over the sidewalls of the wires,” says Dr. Frank-J. Meyer zu Heringdorf in describing the idea behind the research. He has now been able to confirm his assumption in an experiment conducted in collaboration with the IBM Research Lab in Yorktown Heights (USA).
Surprisingly, the zigzag patterns differ according to the quantity of gold. The researchers are currently concerned with finding out more about these fine distinctions: the quantity of gold on the sidewalls of the wires is less than a single layer of atoms.
Last year, an innovative interferometer was built to examine silver nano-islands. In a pump-probe experiment, it was possible to depict the propagation of surface plasmon waves directly as a function of time, with time discretisation of one attosecond (the millionth part of a millionth part of one microsecond).