1. School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore
2. Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore
3. School of Optoelectronic Engineering and Instrumentation Science, Dalian University of Technology, Dalian 116024, P.R. China
4. Physical Science and Engineering Division, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia
5. School of Physics, Dalian University of Technology, Dalian 116024, P.R. China
6. Institute for Digital Molecular Analytics and Science, Nanyang Technological University, Singapore 639798, Singapore