1. School of Physics & Optoelectric Engineering, Guangdong University of Technology, Guangzhou Higher Education Mega Centre, Guangzhou 510006, P. R. China
2. School of Materials and Energy, Guangdong University of Technology, Guangzhou Higher Education Mega Centre, Guangzhou 510006, P. R. China
3. NIH Transducer Resource Center and Department of Biomedical Engineering, University of Southern California, USA