1. Center
of Materials Physics and Chemistry, and Department of Physics, Beihang University, Beijing 100191, P. R. China
2. Institute
for Superconducting and Electronic Materials, University of Wollongong, Wollongong
NSW 2522, Australia
3. Key
Laboratory of Photochemical Conversion and Optoelectronic Materials,
and HKU-CAS Joint Laboratory on New Materials, Technical Institute
of Physics and Chemistry, Chinese Academy of Sciences (CAS), Beijing 100190, P. R. China
4. College
of Chemistry, Jilin University, Changchun 130012, P. R. China
5. Beijing
Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, P. R. China