1. Department
of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551, Singapore
2. Institute
of Materials Research and Engineering, Agency for Science Technology and Research, 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Singapore
3. Centre
for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore 117542, Singapore
4. Institute
of High Performance Computing, Agency for Science Technology and Research, 1 Fusionopolis Way, #16-16 Connexis, Singapore 138632, Singapore