1. Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore
2. Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543, Singapore
3. Centre for Advanced 2D Materials, National University of Singapore, Block S14, 6 Science Drive 2, Singapore 117546, Singapore
4. NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, 13 Centre for Life Sciences, #05-01, 28 Medical Drive, Singapore 117456, Singapore
5. State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics, Sun Yat-sen University, Guangzhou 510275, Guangdong, People’s Republic of China
6. Department of Applied Physics, the Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, People’s Republic of China
7. Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Singapore
8. NUSNNI-NanoCore, National University of Singapore, 117411, Singapore
9. Department of Materials Science & Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117575, Singapore
10. Department of Electrical and Computer Engineering, National University of Singapore, 9 Engineering Drive 1, 117575, Singapore