1. The Hong Kong Polytechnic University Shenzhen Research Institute; Shenzhen Guangdong China
2. Department of Applied Physics; The Hong Kong Polytechnic University; Hung Hom Kowloon Hong Kong China
3. School of Physics and Engineering; and Key Laboratory of Material Physics of Ministry of Education; Zhengzhou University; Zhengzhou Henan 450052 China
4. School of Electronic Science and Applied Physics; Hefei University of Technology; Hefei Anhui 230009 China
5. School of Materials Science and Engineering; Zhengzhou University; Zhengzhou Henan 450052 P. R. China
6. University Research Facility in Materials Characterization and Device Fabrication; The Hong Kong Polytechnic University; Hung Hom Kowloon Hong Kong China