1. Department of Physics
2. COMSATS University Islamabad
3. Pakistan
4. Department of Chemistry
5. Faculty of Physics and Center for Nanointegration Duisburg-Essen (CENIDE)
6. University of Duisburg-Essen
7. 47057 Duisburg
8. Germany
9. University of Science and Technology of China
10. Hefei 230026
11. P. R. China