1. Institute of Materials Research and Engineering; Agency for Science,; Technology and Research (A*STAR); 2 Fusionopolis Way, Innovis, #08-03 Singapore 138634 Singapore
2. Educational Research Institute of Nanostructures and Biosystems; N. G. Chernyshevsky Saratov State University; 83 Astrakhanskaya Street Saratov 410012 Russia
3. Centre for Advanced 2D Materials; National University of Singapore; 6 Science Drive 2 Singapore 117546 Singapore
4. Biophotonics Lab Center of Photonics & Quantum Materials; Skolkovo Institute of Science and Technology; Nobel Str. 3 Moscow 143026 Russia
5. School of Engineering and Materials Science; Queen Mary University of London; Mile End Road London E1 4NS UK