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