1. Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543
2. Centre
for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117546
3. NUS
Graduate School for Integrative Sciences and Engineering, National University of Singapore, 28 Medical Drive, Singapore 117456
4. Department of Physics, National University of Singapore, 3 Science Drive 2, Singapore 117542