1. National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, People's Republic of China
2. Ecomaterials and Renewable Energy Research Center (ERERC) at School of Physics, Nanjing University, Nanjing 210093, People's Republic of China
3. College of Engineering and Applied Sciences, Nanjing University, Nanjing 210093, People's Republic of China
4. Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, People's Republic of China
5. Jiangsu Provincial Key Laboratory for Nanotechnology, Nanjing University, Nanjing 210093, People's Republic of China