1. Bundesanstalt für Materialforschung und -prüfung (BAM), Unter den Eichen 87, Berlin 12205, Germany
2. Institute of Physics and Astronomy, University of Potsdam, Karl-Liebknecht-Straße 24-25, Potsdam 14476, Germany
3. Department of Mechanical and Aerospace Engineering, New Mexico State University, Las Cruces, New Mexico 8001, USA