1. School of Materials Science & Engineering, Nanyang Technological University, Singapore 639798, Singapore
2. Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
3. University of Chinese Academy of Sciences, Beijing 100049, China
4. Department of Electronic Engineering, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR, China
5. Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
6. CINTRA CNRS/NTU/THALES, UMI 3288, Singapore 637553, Singapore
7. School of Materials Science and Engineering, School of Physical and Mathematical Science and School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore