1. Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551, Singapore
2. State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, China
3. Songshan Lake Materials Laboratory, Songshan Lake Mat Lab, Dongguan 523808, China
4. Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117583, Singapore
5. Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore