1. Institute of Physics and Center for Nanotechnology, University of Münster, 48149 Münster, Germany
2. Institute of Solid State Theory, University of Münster, 48149 Münster, Germany
3. Institute of Mineralogy, University of Münster, 48149 Münster, Germany
4. European Synchrotron Radiation Facility, 38043 Grenoble, France
5. Faculty of Natural Sciences, Institute of Earth Sciences, University of Silesia, Sosnowiec 41-200, Poland
6. Insitut für Anorganische und Analytische Chemie, University of Münster, 48149 Münster, Germany
7. Nanophotonics Lab, Department of Physics, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India