1. State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Department of Physics, Collaborative Innovation Center of Advanced Microstructures, Fudan University, Shanghai 200433, People's Republic of China
2. Department of Physics, Shanghai University, Shanghai 200444, People's Republic of China
3. Laboratory of Advanced Materials, Department of Chemistry, Fudan University, Shanghai 200433, People's Republic of China
4. Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210, People's Republic of China