1. Freiburg Materials Research
Center, University of Freiburg, Stefan-Meier-Strasse
21, 79104 Freiburg, Germany
2. Fraunhofer Institute for Mechanics of Materials IWM, Wöhlerstrasse
11, 79108 Freiburg, Germany
3. School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430,
United States
4. Lehrstuhl
für Physikalische
Chemie, Technische Universität München, Lichtenbergstrasse 4, 85748 Garching, Germany