1. Department of Physics National University of Singapore Singapore 117551 Singapore
2. Centre for Bioimaging Sciences and Department of Biological Sciences National University of Singapore Singapore 117557 Singapore
3. Centre for Advanced 2D Materials and Graphene Research Centre National University of Singapore Singapore 117546 Singapore
4. Department of Chemistry University of Illinois at Chicago Chicago IL 60607 USA
5. NUSNNI‐NanoCore National University of Singapore Singapore 117411 Singapore
6. Department of Physics Department of Biopharmaceutical Sciences University of Illinois at Chicago Chicago IL 60607 USA