1. Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543, Singapore
2. Graphene Research Centre, National University of Singapore, 2 Science Drive 3, 117542, Singapore
3. Department of Physics, National University of Singapore, 2 Science Drive 3, 117542, Singapore
4. Institute of Materials Research and Engineering, 3 Research Link, 117602, Singapore
5. NanoCore, National University of Singapore, Singapore 117576, Singapore