1. Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543, Singapore
2. National University of Singapore (Suzhou) Research Institute, 377 Lin Quan Street, Suzhou Industrial Park, Suzhou, Jiangsu 215123, P. R. China
3. Joint School of National University of Singapore and Tianjin University, International Campus of Tianjin University, Binhai New City, Fuzhou 350207, P. R. China
4. Agency for Science, Technology and Research (A*STAR), Institute of Materials Research and Engineering (IMRE), Innovis, 138634, Singapore
5. Department of Physics, National University of Singapore, 2 Science Drive 3, 117542, Singapore