1. Department of PhysicsNational University of Singapore 2 Science Drive 3 Singapore 117551 Singapore
2. Centre for Advanced 2D MaterialsNational University of Singapore 6 Science Drive 2 Singapore 117546 Singapore
3. Department of ChemistryNational University of Singapore 2 Science Drive 3 Singapore 117543 Singapore
4. National Institute for Material Science 1‐1 Namiki Tsukuba 305‐0044 Japan