1. Department of Applied PhysicsThe Hong Kong Polytechnic University Hung Hom, Kowloon Hong Kong P. R. China
2. Laboratory for Advanced Interfacial Materials and DevicesInstitute of Textiles and ClothingThe Hong Kong Polytechnic University Hung Hom Hong Kong P. R. China
3. State Key Laboratory of High Performance Ceramics and Superfine MicrostructureShanghai Institute of CeramicsChinese Academy of Sciences Shanghai 200050 China
4. The Hong Kong Polytechnic University Shenzhen Research Institute Shenzhen 518057 P. R. China