1. Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551, Singapore
2. Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
3. Singapore Synchrotron Light Source (SSLS), National University of Singapore, Singapore 117603, Singapore
4. Shanghai Key Laboratory of High Temperature Superconductors, Physics Department, Shanghai University, Shanghai 200444, China
5. Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research), 2 Fusionopolis Way, Singapore 138634, Singapore