1. Department of Mechanical and Biomedical Engineering; City University of Hong Kong; 83 Tat Chee Ave Kowloon Hong Kong SAR 999077 P. R. China
2. Department of Physics and Material Science; City University of Hong Kong; 83 Tat Chee Ave Kowloon Hong Kong SAR 999077 P. R. China
3. Shenzhen Research Institute; City University of Hong Kong; Shenzhen 518057 P. R. China