1. Department of Physics, National University of Singapore, 2 Science Drive 3, 117542 Singapore
2. Center for Advanced 2D Materials, National University of Singapore, 6 Science Drive 2, 117546 Singapore
3. ANTARES Beamline, Synchrotron SOLEIL and Université Paris-Saclay, L’Orme des Merisiers, 91192 Gif sur Yvette, Cedex, France
4. Key Laboratory for Intelligent Nano Materials and Devices of Ministry of Education, and Institute of Nanoscience, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
5. Instituto de Materiales de Madrid, CSIC, C/Sor Juana Inés de la Cruz, 3 Cantoblanco, 28049 Madrid, Spain
6. School of Physics, Southeast University, 2 Southeast University Road, Nanjing 211189, China