1. Department of Physics and Institute of Advanced Materials Hong Kong Baptist University Kowloon Tong Hong Kong SAR P. R. China
2. School of Physics Shandong University Jinan Shandong 250100 China
3. Department of Chemistry Energy Institute and Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration & Reconstruction Hong Kong University of Science and Technology (HKUST) Clear Water Bay Kowloon Hong Kong