1. Institute of Physics; Martin Luther University Halle-Wittenberg; Germany
2. California Institute of Technology; Pasadena; California 91125 USA
3. Colorado School of Mines; Golden; Colorado 80401 USA
4. CRISMAT UMR 6508; ENSICAEN; Caen and LIED, URD 0001, University Paris VII, France
5. Institute of Materials Research; German Aerospace Center (DLR); 51170 Köln Germany
6. Justus Liebig University Giessen; Institute of Inorganic and Analytical Chemistry; 35392 Giessen Germany