1. Department of Physics
2. University of Science and Technology Beijing
3. Beijing 100083
4. China
5. National University of Singapore
6. Singapore 117411
7. Singapore
8. Centre for Advanced 2D Materials and Graphene Research Centre
9. Singapore 117546
10. Institute of Materials Research and Engineering
11. Department of Mechanical Engineering & Engineering Science Programme
12. Singapore 117575
13. Department of Materials Science and Engineering