1. National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures, School of Physics, Nanjing University, Nanjing 210093, P. R. China
2. Eco-Materials and Renewable Energy Research Center (ERERC), Jiangsu Key Laboratory for Nano Technology, Nanjing University, Nanjing 210093, P. R. China
3. Department of Food Science, Rutgers University, 65 Dudley Road, New Brunswick, New Jersey 08901, United States
4. Department of Materials Science and Engineering, Anhui Polytechnic University, Wuhu 241000, P. R. China
5. Kunshan Innovation Institute of Nanjing University, Kunshan, Jiangsu 215347, P. R. China
6. Faculty of Informatics and Engineering, The University of Electro-Communications, Tokyo 182-8585, Japan