1. German Aerospace Center (DLR), Institute of Materials Research, Cologne, Germany
2. European Astronaut Center, European Space Agency (ESA), Linder Hoehe, 51147 Cologne, Germany
3. Justus Liebig University Giessen, Institute of Inorganic and Analytical Chemistry, D-35392 Giessen, Germany
4. University of Duisburg-Essen, Institute of Technology for Nanostructures (NST) and CENIDE, D-47057 Duisburg, Germany