1. Condensed Matter Science and Technology Institute, Harbin Institute of Technology, Harbin 150080, China
2. Department of Instrument Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
3. Department of Chemistry, Harbin Institute of Technology, Harbin 150080, China
4. Department of Mathematics and Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, USA