1. Institute of Nanostructure and Solid State Physics, Universität Hamburg, 20355 Hamburg, Germany
2. Institute for Microtechnologies, RheinMain University of Applied Sciences Wiesbaden, 65428 Ruesselsheim, Germany
3. Leibniz Institute for Solid State and Materials Research (IFW) Dresden, P.O. Box 270116, 01171 Dresden, Germany
4. Department of Microsystems Engineering–IMTEK, University of Freiburg, Georges-Koehler-Allee 102, 79110 Freiburg, Germany