1. EMPA Materials Science and Technology, Feuerwerkerstrasse 39, 3602 Thun, Switzerland, Max Planck Institute of Microstructure Physics, Weinberg 2, 06120 Halle, Germany, Martin-Luther Universität Halle Wittenberg, Friedemann-Bach-Platz 6, 06099 Halle, Germany, and Institute of Microtechnology, University of Neuchâtel, A.-L. Breguet 2, 2000 Neuchâtel, Switzerland