1. International Collaborative Laboratory of 2D Materials for Optoelectronic Science & Technology of Ministry of Education, Institute of Microscale Optoeletronics, Shenzhen University, Shenzhen 518060, China
2. Department of Materials Science and Engineering, National University of Singapore, Singapore 117575, Singapore
3. Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, No. 19 Yuquan Road, Beijing, P.R. China
4. School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459, Singapore