1. Energy Research Institute at NTU (ERI@N) and Interdisciplinary Graduate School, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798
2. School of Physical and Mathematical Sciences, Division of Physics and Applied Physics, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
3. Department of Physics and Astronomy and London Centre for Nanotechnology, University College London, London WC1E 6BT, United Kingdom
4. Dipartimento di Chimica e Chimica Industriale, Università degli Studi di Genova, via Dodecaneso 31, 16121 Genova, Italy