1. Department of Materials Science and Engineering, Faculty of Engineering, National University of Singapore, 117574 Singapore
2. Department of Physics, National University of Singapore, 117551 Singapore
3. Department of Chemistry and Shenzhen Grubbs Institute, Southern University of Science and Technology (SUSTech), Shenzhen 518055, China
4. Institute of Chemical and Engineering Sciences, Agency for Science, Technology and Research (A*STAR), 1 Pesek Road, Jurong Island, 627833 Singapore
5. Department of Mechanical Engineering, National University of Singapore, 117575 Singapore