1. Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117583, Singapore
2. Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
3. Department of Physics, Kannur University, Swami Anandatheertha Campus-Payyanur, Kannur-670327, Kerala India
4. Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore
5. Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore
6. Hybrid Materials for Optoelectronics Group, Department of Molecules and Materials, MESA+ Institute for Nanotechnology and Center for Brain-Inspired Nano Systems, Faculty of Science and Technology, University of Twente, 7500 AE Enschede, The Netherlands