1. Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Materials Science and Engineering, Hunan University, Changsha, Hunan 410082, PR China
2. School of Physics and Electronics, Hunan University, Changsha, Hunan 410082, PR China
3. State Key Laboratory of Superhard Materials, Key Laboratory of Automobile Materials of MOE, and School of Materials Science and Engineering, Jilin University, Changchun 130012, PR China
4. Department of Chemistry, University of Wisconsin−Madison, Madison, Wisconsin 53706, United States
5. College of Electrical and Information Engineering, Hunan University, Changsha, Hunan 410082, PR China