1. Centre
for Advanced 2D Materials (CA2DM) and Department of Chemistry, National University of Singapore, Singapore 117546
2. The
Blackett Laboratory, Department of Physics, Imperial College London, London SW7 2AZ, United Kingdom
3. NUS
Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore 117456
4. Department
of Physics and Singapore Synchrotron Light Source, National University of Singapore, Singapore 119077
5. Fakultät
für Physik, Ludwigs-Maximilians-Universität München, 80799 München, Germany