1. Centre for Micro-Photonics, Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia
2. College of Electronic Science and Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210023, China
3. Plasma Sources and Application Center, NIE, Nanyang Technological University, 1 Nanyang Walk, Singapore 637616, Singapore
4. Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research), 3 Research Link, Singapore 117602, Singapore