1. Department
of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore, Singapore 117543
2. Centre
for Advanced 2D Materials (CA2DM) and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore, Singapore 117546
3. NUS Graduate School for Integrative Sciences and Engineering, 28 Medical Drive #05-01, Singapore, Singapore 117597
4. Pacific Northwest National Laboratory, Richland, Washington 99352, USA
5. Institute of Materials Research and Engineering, 2 Fusionopolis Way, #08-03 Innovis, Singapore, Singapore 138634