1. School
of Metallurgy and Environment, Central South University, Changsha 410083, People’s Republic of China
2. Department
of Applied Physics, The Hong Kong Polytechnic University, Kowloon, Hong Kong, People’s Republic of China
3. School
of Physical and Electronic Science, Changsha University of Science and Technology, Changsha 410004, Hunan, People’s Republic of China
4. University
Research Facility in Materials Characterization and Device Fabrication, The Hong Kong Polytechnic University, Kowloon, Hong Kong, People’s Republic of China
5. Shanghai
Institute of Microsystem and Information Technology, Chinese Academy of Science, Shanghai 200050, People’s Republic of China