1. CAS Center for Excellence in Nanoscience, Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 100083, P. R. China
2. School of Nanoscience and Technology, University of Chinese Academy of Sciences, Beijing 100049, P. R. China
3. Innovative Center for Advanced Materials, Hangzhou Dianzi University, Hangzhou 310018, China
4. Laboratory for Advanced Materials and Electron Microscopy, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
5. Canadian Light Source Inc., University of Saskatchewan, Saskatoon, SK S7N 2V3, Canada
6. Beijing Key Laboratory for Green Catalysis and Separation, College of Environmental and Energy Engineering, Beijing University of Technology, Beijing 100124, P. R. China
7. Center on Nanoenergy Research, School of Physical Science and Technology, Guangxi University, Nanning 530004, China
8. School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245, United States