1. State Key Laboratory of High Performance Ceramics and Superfine Microstructure Shanghai Institute of Ceramics Chinese Academy of Sciences Shanghai 200050 P. R. China
2. Department of Applied Physics The Hong Kong Polytechnic University Hong Kong 999077 P. R. China
3. School of Materials Science and Engineering and Jiangxi Engineering Laboratory for Advanced Functional Thin Films Nanchang University Nanchang 330031 P. R. China
4. Hefei National Laboratory for Physical Sciences at the Microscale University of Science and Technology of China Hefei 230026 P. R. China
5. School of Physics and Materials Science Guangzhou University Guangzhou 510006 P. R. China