1. Department of Physics, Beijing Normal University, Beijing 100875, China
2. Department of Basic Courses, Tianjin Sino-German University of Applied Sciences, Tianjin 300350, China
3. Graduate School of Excellence Materials Science in Mainz, Staudingerweg 9, D-55128 Mainz, Germany
4. Institut für Physik, Johannes Gutenberg-Universität Mainz, Staudingerweg 9, D-55099 Mainz, Germany
5. Department of Physics, American University of Beirut, P. O. Box 11-0236, Beirut 1107 2020, Lebanon
6. Institute for Macromolecular Compounds RAS, Bolshoi pr. 31, 199004 St. Petersburg, Russia
7. Chemical-Pharmaceutical Academy, Professora Popova 14, 197022 St. Petersburg, Russia