1. National Laboratory of Solid State Microstructures
2. Nanjing University
3. Nanjing 210093, P. R. China
4. Eco-Materials and Renewable Energy Research Center (ERERC)
5. Department of Physics
6. Kunshan Innovation Institute of Nanjing University
7. Kunshan 215347, P. R. China
8. Department of Materials Science and Engineering