1. Department of Materials Science and Engineering, City University of Hong Kong, Kowloon 999077, Hong Kong
2. Shenzhen Research Institute, City University of Hong Kong, Shenzhen 518057, P. R. China
3. Center for Applied Chemical Research, Frontier Institute of Science and Technology, Xi’an Jiaotong University, Xi’an 710049, P. R. China
4. Department of Physics, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan