1. Institute of Nanotechnology Karlsruhe Institute of Technology Hermann‐von‐Helmholtz Platz 1 76344 Eggenstein‐Leopoldshafen Germany
2. Institute of Materials Science Technische Universität Darmstadt Alarich‐Weiss‐Straße 2 64287 Darmstadt Germany
3. Materials Science and Engineering Division National Institute of Standards and Technology Gaithersburg MD 20899 USA
4. Light Technology Institute Karlsruhe Institute of Technology Engesserstraße 13 76131 Karlsruhe Germany
5. Institute of Microstructure Technology Karlsruhe Institute of Technology Hermann‐von‐Helmholtz‐Platz 1 76344 Eggenstein‐Leopoldshafen Germany
6. Quantum Measurement Division National Institute of Standards and Technology Gaithersburg MD 20899 USA