1. Beijing Advanced Innovation Center for Materials Genome Engineering Key Laboratory for Renewable Energy Beijing Key Laboratory for New Energy Materials and Devices Institute of Physics Chinese Academy of Sciences Beijing 100190 China
2. School of Physical Sciences University of Chinese Academy of Sciences Beijing 100190 China
3. State Key Laboratory for Surface Physics Institute of Physics Chinese Academy of Sciences Beijing 100190 China
4. Stanford Synchrotron Radiation Lightsource SLAC National Accelerator Laboratory Menlo Park CA 94025 USA