1. Department of Materials Science and Engineering, National University of Singapore, Singapore 117575, Singapore
2. Institute for Microelectronics Technology, Russian Academy of Sciences, Chernogolovka 142432, Russia
3. Centre for Advanced 2D Materials, National University of Singapore, Singapore 117546, Singapore
4. National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
5. Chongqing 2D Materials Institute, Liangjiang New Area, Chongqing 400714, China