1. School of Physics, University of Electronic Science and Technology of China, Chengdu 610054, P. R. China
2. Research School of Chemistry, Australian National University, Canberra, ACT 2601, Australia
3. Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of Education, School of Energy and Power Engineering, Dalian University of Technology, Dalian 116024, P. R. China
4. Institute of Materials Science, Technical University of Darmstadt, Darmstadt 64287, Germany
5. School of Physics, National University of Singapore, Singapore 119077, Singapore
6. School of Civil Engineering and Surveying, Southwest Petroleum University, Chengdu 610500, P. R. China
7. School of Civil Engineering, Hebei University of Engineering, Handan 056038, P. R. China