1. Department of Materials Science and EngineeringCity University of Hong Kong 83 Tat Chee Avenue Kowloon Hong Kong 999077 P. R. China
2. School of Material and EnergyGuangdong University of Technology Guangzhou 510006 P. R. China
3. Chengdu Research InstituteCity University of Hong Kong Chengdu 610200 P. R. China