1. Department
of Chemistry, National University of Singapore, Singapore 117543, Singapore
2. NUS
Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore 117456, Singapore
3. Center
for Advanced 2D Materials and Graphene Research Center, National University of Singapore, Singapore 117546, Singapore
4. Institute
of Materials Research and Engineering, Agency for Science, Technology and Research, Singapore 117602, Singapore
5. Department
of Physics, National University of Singapore, Singapore 117551, Singapore