1. Division of Physics and Applied Physics,
School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore
2. Energy Research Institute @NTU (ERI@N), Research Techno Plaza, X-Frontier Block, Level 5, 50 Nanyang Drive, Singapore 637553, Singapore
3. College of Physics and Electronics, Shandong Normal University, 88 East Wenhua Road, Jinan 250014, People’s Republic of China
4. School of Materials Science and Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Singapore
5. Laboratory of Photonics
and Interfaces, Department of Chemistry and Chemical Engineering, Swiss Federal Institute of Technology, Station 6, CH-1015 Lausanne, Switzerland
6. Department
of Materials Science and Engineering, University of California, 210 Hearst
Memorial Mining Building, Berkeley, California 94720, United States