1. Materials Interference CenterShenzhen Institutes of Advanced TechnologyChinese Academy of Sciences Shenzhen 518055 P.R. China
2. Shenzhen College of Advanced TechnologyUniversity of Chinese Academy of Sciences Shenzhen 518055 P.R. China
3. Department of Physics and Department of Materials Science and EngineeringCity University of Hong Kong Tat Chee Avenue Kowloon, Hong Kong P.R. China