1. Materials and Interfaces Center Shenzhen Institutes of Advanced Technology Chinese Academy of Sciences Shenzhen 518055 P. R. China
2. Institute of Nanophotonics Jinan University Guangzhou 511443 P. R. China
3. Shenzhen College of Advanced Technology University of Chinese Academy of Sciences Shenzhen 518055 P. R. China
4. Department of Physics Department of Materials Science and Engineering and Department of Biomedical Engineering City University of Hong Kong Tat Chee Avenue Kowloon Hong Kong 999077 China