1. School of Material and Energy Guangdong University of Technology Guangzhou 510006 P.R. China
2. Institute of Semiconductors South China Normal University Guangzhou 510631 P.R. China
3. Department of Chemistry The Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration and Reconstruction Institute for Advanced Study and Department of Chemical and Biological Engineering The Hong Kong University of Science and Technology Clear Water Bay, Kowloon Hong Kong China
4. School of Materials and Chemical Engineering Anhui Jianzhu University Hefei 230601 P.R. China
5. Department of Chemistry University of Hull Cottingham Road Hull Yorkshire HU6 7RX UK
6. Laboratory for Soft Machines & Electronics Departments of Mechanical Engineering Electrical and Computer Engineering Michigan State University East Lansing MI 48824 USA