1. A Singapore Berkeley Research Initiative for Sustainable Energy, Berkeley Educational Alliance for Research in Singapore, 1 CREATE Way, 138602 Singapore
2. NUSNNI-Nanocore, National University of Singapore, 117411 Singapore
3. Yale Energy Sciences Institute and Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
4. Department of Chemistry, Faculty of Science, National University of Singapore, 3 Science Drive 3, 117543 Singapore
5. Department of Physics, National University of Singapore, 117542 Singapore
6. Centre for Advanced 2D Materials, National University of Singapore, 6 Science Drive 2, 117546 Singapore
7. Department of Electrical and Computer Engineering, National University of Singapore, 117576 Singapore
8. Department of Integrative Science and Engineering, National University of Singapore, 117456 Singapore