1. Department of Physics, Ningbo University, Ningbo, Zhejiang 315211, China
2. School of Material Science and Chemical Engineering, Institute of Mass Spectrometry, Ningbo University, Ningbo 315211, China
3. Department of Physics, Hefei University of Technology, Hefei, Anhui 230009, China
4. Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
5. Department of Materials Science & Engineering, City University of Hong Kong, Kowloon 999077, Hong Kong, China