1. Department of ChemistryNational University of Singapore 3 Science Drive 3 Singapore 117543 Singapore
2. Department of PhysicsNational University of Singapore 2 Science Drive 3 Singapore 117542 Singapore
3. Hefei National Laboratory for Physical Sciences at the MicroscaleCAS Centre for Excellence and Synergetic Innovation Center of Quantum Information and Quantum PhysicsUniversity of Science and Technology of China Hefei 230026 China
4. Center for Functional Nanomaterials Brookhaven National Laboratory Upton NY 11973 USA
5. Center for Advanced 2D Materials and Graphene Research CenterNational University of Singapore 3 Science Drive 3 Singapore 117546 Singapore
6. Institute for Advanced Study and Department of PhysicsNanchang University 999 Xue Fu Da Dao Nanchang 330031 China
7. National University of Singapore (Suzhou) Research Institute 377 Lin Quan Street Suzhou Industrial Park Jiangsu 215123 China