1. Energy Research Institute @NTU (ERI@N); Research Techno Plaza, X-Frontier Block, Level 5, 50 Nanyang Drive Singapore 637553 Singapore
2. School of Materials Science and Engineering; Nanyang Technological University; Nanyang Avenue Singapore 639798 Singapore
3. Institute of Materials Research and Engineering (IMRE); Agency of Science Technology and Research (A*STAR); 3 Research Link Singapore 117602 Singapore
4. School of Physical and Mathematical Sciences; Nanyang Technological University; 21 Nanyang Link Singapore 637371 Singapore
5. Department of Materials Science and Engineering; University of California; Berkeley USA
6. Laboratory of Photonics and Interfaces, EPFL; Lausanne Switzerland