1. Department of Physics and Research Center OPTIMAS Technische Universität Kaiserslautern P.O. Box 3049 67653 Kaiserslautern Germany
2. Institute of Physical Chemistry Karlsruhe Institute of Technology Fritz-Haber-Weg 2 76131 Karlsruhe Germany
3. Institute of Inorganic Chemistry Karlsruhe Institute of Technology Engesserstrasse 15 76131 Karlsruhe Germany
4. Institute of Nanotechnology Karlsruhe Institute of Technology Hermann-von-Helmholtz-Platz 1 76344 Eggenstein-Leopoldshafen Germany
5. School of Mechanics Civil Engineering and Architecture Northwestern Polytechnical University Xi'an 710072 China