1. Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, 315201 Ningbo, P. R. China
2. Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, P. R. China
3. Department of Chemical and Biomolecular Engineering, Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, United States