1. Department of Chemistry, National University of Singapore, 117543, Singapore
2. Institute for Functional Intelligent Materials, National University of Singapore, 117544, Singapore
3. Centre for Advanced 2D Materials, National University of Singapore, 117543, Singapore
4. Department of Physics, National University of Singapore, 2 Science Drive 3, 117542, Singapore
5. Yale-NUS College, 16 College Avenue West, 138527, Singapore
6. Department of Physics, University of California, Berkeley94720, California, United States
7. Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba305-0044, Japan
8. International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba305-0044, Japan
9. Institute of Materials Research and Engineering, Agency for Science, Technology and Research, 08-03, 2 Fusionopolis Way, Singapore138634, Singapore