1. Department of Physics, National University of Singapore, 117551 Singapore, Singapore
2. Centre for BioImaging Sciences, Department of Biological Sciences, National University of Singapore, 117557 Singapore, Singapore
3. AIXTRON SE, Herzogenrath 52134, Germany
4. Centre for Advanced 2D Materials, National University of Singapore, 117546 Singapore, Singapore
5. Department of Materials Science and Engineering, National University of Singapore, 117575 Singapore, Singapore