1. Department of Materials Science and Engineering, National University of Singapore, 117574 Singapore, Singapore
2. Division of Advanced Materials, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, 215123 Suzhou, P. R. China
3. College of Environment and Energy, South China University of Technology, 510000 Guangzhou, P. R. China
4. Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, 117585 Singapore, Singapore
5. Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, 100049 Beijing, P. R. China