1. The Blackett Laboratory, Department of Physics, Imperial College London, London SW7 2AZ, United Kingdom
2. Centre for Advanced 2D Materials (CA2DM) and Department of Chemistry, National University of Singapore, Singapore 117543, Singapore
3. NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore 117456, Singapore
4. School of Photovoltaic and Renewable Energy Engineering, University of New South Wales, Sydney, NSW 2052, Australia
5. Chair in Hybrid Nanosystems, Nanoinstitute Munich, Faculty of Physics, Ludwig-Maximilians-Universität München, 80539 München, Germany