1. Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore.
2. Institute of Chemical and Engineering Sciences, Agency for Science, Technology and Research (A*STAR), 1 Pesek Road, Jurong Island, Singapore 627833, Singapore.
3. Department of Physics, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore.
4. School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459, Singapore.
5. Department of Materials Science and Engineering, National University of Singapore, Singapore 117575, Singapore.
6. State Key Laboratory of Solidification Processing, Center for Nano Energy Materials, Northwestern Polytechnical University, Xi’an 710072, China.