1. Department of Chemistry, and Centre for Advanced 2D Materials, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
2. Department of Chemistry and Biochemistry, University of Alabama, Tuscaloosa, Alabama 35487-0336, United States
3. Savannah River National Laboratory, Aiken, South Carolina 29808, United States
4. Hybrid Materials for Opto-Electronics 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, P.O. Box 217, 7500 AE Enschede, The Netherlands