1. Collaborative Innovation Center of Advanced Microstructures, National Laboratory of Solid State Microstructures, School of Physics, Nanjing University, Nanjing, Jiangsu 210093, People’s Republic of China
2. Eco-materials and Renewable Energy Research Center, College of Engineering and Applied Sciences, Nanjing University, Nanjing, Jiangsu 210093, People’s Republic of China
3. Jiangsu Key Laboratory for Nano Technology, School of Physics, Nanjing University, Nanjing, Jiangsu 210093, People’s Republic of China