1. School of Science, Tianjin University of Technology, Tianjin 300384, China
2. Tianjin International Center for Nanoparticles and Nanosystems, Tianjin University, Tianjin 300072, China
3. School of Physics and Electronics, Shandong Normal University, Jinan 250358, China
4. International Iberian Nanotechnology Laboratory (INL), Ave. Mestre Jose Veiga, 4715-330 Braga, Portugal