1. Shenzhen Institute of Advanced Technology Chinese Academy of Sciences Shenzhen 518055 P. R. China
2. University of Chinese Academy of Sciences Beijing 100049 P. R. China
3. Department of Electrical and Electronic Engineering Southern University of Science and Technology 1088 Xueyuan Avenue 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 P. R. China