1. Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore
2. Department of Physics, National University of Singapore, Singapore 117551, Singapore
3. Department of Mechanical Engineering, National University of Singapore, Singapore 117575, Singapore
4. National University of Singapore (Chongqing) Research Institute, Chongqing 401123, China