1. Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, 637371, Singapore
2. Institute of Chemical and Engineering Sciences, A*STAR, 1 Pesek Road, Jurong Island, Singapore 627833, Singapore
3. Department of Mechanical Engineering and Materials Science and Engineering Program, University of Texas at Austin, One University Station C2200, Austin, Texas 78712, United States
4. Department of Physics, Faculty of Science, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore