1. School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore
2. School of Physical and Mathematical Sciences & School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore
3. State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China
4. Department of Materials Science and Engineering, National University of Singapore, Singapore 117575, Singapore
5. School of Computer Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore