1. Contribution from the Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117576, Department of Chemistry, University of Liverpool, Crown Street, Liverpool L69 3BX, United Kingdom, Nanoscience and Nanotechnology Initiative, National University of Singapore, 2 Engineering Drive 3, Singapore 117576, and Physics Department, National University of Singapore, 2 Science Drive 3, Singapore 117542