1. Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543
2. Department of Materials Science and Engineering, National University of Singapore, Faculty of Engineering, 7 Engineering Drive 1, Singapore 117574
3. Singapore−MIT Alliance, E4-04-10, 4 Engineering Drive 3, Singapore 117576
4. Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542
5. Institute of Materials Research and Engineering, 3 Research Link, Singapore 117602