1. Division of Physics and Applied Physics; School of Physical and Mathematical Sciences; Nanyang Technological University; 21 Nanyang Link Singapore 637371 Singapore
2. School of Materials Science and Engineering; Nanyang Technological University; Nanyang Avenue 639798 Singapore
3. Energy Research Institute @NTU (ERI@N); Research Techno Plaza, X-Frontier Block, Level 5; 50 Nanyang Drive Singapore 637553 Singapore