1. Department
of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542
2. Center
For Advanced 2D
Materials and Graphene Research
Center, National University of Singapore, 6 Science Drive 2, Singapore 117546
3. Institute of Materials
Research and Engineering,
A*STAR (Agency for Science, Technology and Research), 3 Research Link, Singapore 117602
4. Department
of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543