1. Department
of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
2. Materials
and Surface Science Institute and Department of Physics and Energy, University of Limerick, Limerick, Ireland
3. Centre
for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore
4. Solar Energy Research Institute of Singapore, 7 Engineering Drive 1, Singapore 117574, Singapore