1. Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China
2. Department of Physics, Tamkang University, Tamsui, New Taipei City 25137, Taiwan, R.O.C.
3. Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Strasse 40, Dresden 01187, Germany
4. University of Chinese Academy of Sciences, Beijing 100049, China
5. National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan, R.O.C.