1. Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Singapore 138634, Republic of Singapore
2. Department of Chemistry, University of Southampton, University Road, Highfield, Southampton SO17 1BJ, United Kingdom
3. Department of Physics, Faculty of Science, National University of Singapore, 2 Science Drive 3, Singapore 117551, Republic of Singapore
4. Department of Electrical and Computer Engineering, Faculty of Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117583, Republic of Singapore
5. School of Material Science and Engineering, Nanyang Technological University, Block N4.1, 50 Nanyang Avenue, Singapore 639798, Republic of Singapore