1. Division of Physics and Applied Physics; School of Physical and Mathematical Sciences; Nanyang Technological University; Singapore 637371 Singapore
2. School of Materials Science and Engineering; Nanyang Technological University; Singapore 639798 Singapore
3. Heterogeneous Catalysis; Institute of Chemical Engineering and Sciences; A*star, 1 Pesek Road Jurong Island 627833 Singapore
4. Centre for Disruptive Photonic Technologies; Nanyang Technological University; Singapore 637371 Singapore