1. Foundation Institute of Materials
Science (IWT), Department of Production Engineering, University of Bremen, Badgasteinerstraße 3, 28359
Bremen, Germany
2. Institute
of Particle Technology, Friedrich−Alexander University, Erlangen−Nürnberg,
Cauerstraße 4, 91058 Erlangen, Germany
3. Institute of Solid State Physics, University of Bremen, Otto−Hahn−Allee
1, 28359 Bremen, Germany