1. Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543
2. Graduate School for Integrative Sciences & Engineering (NGS), National University of Singapore 28 Medical Drive, Singapore 117456
3. Department of Physics, Indian Institute of Science Education and Research, Bhopal 462066, India
4. Institute of Materials Research and Engineering, A*STAR, 2 Fusionopolis Way, Innovis, Singapore 138634
5. School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371