1. Department of Mechanical Engineering, National University of Singapore, Singapore, 9 Engineering Drive 1, 117575, Singapore
2. Department of NanoEngineering, University of California San Diego, 9500 Gilman Dr, La Jolla, CA 92093-0448, San Diego, 0448, USA
3. Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis, #08-03, 138634, Singapore
4. Department of Physics, Faculty of Science, National University of Singapore, Singapore, 2 Science Drive 3, Blk S12, Level 2, 117551, Singapore
5. Department of Chemistry, National University of Singapore, Singapore, Block S8 Level 3, 3 Science Drive 3, 117543, Singapore