1. School of Materials Science and Engineering Nanyang Technological University 50 Nanyang Avenue Singapore 639798 Singapore
2. School of Electrical and Electronic Engineering Nanyang Technological University 50 Nanyang Avenue Singapore 639798 Singapore
3. Department of Materials Science and Engineering Tokyo Institute of Technology 2-12-1 Ookayama, Meguro-ku Tokyo 152-8552 Japan
4. Department of Materials Science and Engineering City University of Hong Kong Kowloon Hong Kong SAR China