1. Institute for Materials Science and Center for Nanointegration Duisburg-Essen (CENIDE)
2. University of Duisburg-Essen
3. 45141 Essen
4. Germany
5. Faculty of Physics and Center for Nanointegration Duisburg-Essen (CENIDE)
6. 47057 Duisburg
7. Institute of Fundamental and Frontier Sciences
8. University of Electronic Science and Technology of China
9. Chengdu 610054
10. P. R. China
11. Department of Physics
12. Quaid-i-Azam University
13. Islamabad
14. Pakistan