1. Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, 637371 Singapore
2. Centre for Advanced 2D Materials, National University of Singapore, 117546 Singapore
3. Department of Chemistry, National University of Singapore, 117543 Singapore
4. School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 Singapore
5. Department of Physics, National University of Singapore, 2 Science Drive 3, 117551, Singapore