1. Faculty of Informatics and Engineering
2. The University of Electro-Communications
3. Tokyo 182-8585
4. Japan
5. School of Materials Science and Engineering
6. Shaanxi Normal University
7. Xi'an 710119
8. China
9. Ecomaterials and Renewable Energy Research Center
10. Jiangsu Key Laboratory for Nano Technology
11. National Laboratory of Solid State Microstructures
12. Nanjing University
13. Nanjing 210093