1. Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371
2. Institute of Materials Research & Engineering, Agency for Science, Technologies and Research, 3 Research Link, Singapore 117602
3. Division of Materials Sciences, School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798
4. NOVITAS, Nanoelectronics Center of Excellence, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798