1. Department of Materials Science and Engineering, National University of Singapore, 9 Engineering Drive, Singapore 117575
2. Centre for Advanced 2D Materials, National University of Singapore, 6 Science Drive 2, Singapore 117546
3. Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
4. Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
5. Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
6. 2-Dimensional Crystal Consortium, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
7. Department of Physics, National University of Singapore, Singapore 117551
8. NUS Graduate School Integrative Sciences and Engineering Programme, National University of Singapore, Singapore 117456