1. Department of Physics, National University of Singapore, 2 Science Drive 3, 117542, Singapore
2. Centre for Advanced 2D Materials, National University of Singapore, Block S14, Level 6, 6 Science Drive 2, 117546, Singapore
3. Institute of Materials Research & Engineering (IMRE), A*STAR (Agency for Science, Technology and Research), 2 Fusionopolis Way, Innovis, 138634, Singapore
4. Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Saudi Arabia
5. Department of Materials Science & Engineering, National University of Singapore, 9 Engineering Drive 1, 117575, Singapore