[1]Key Laboratory of Polymer Chemistry and Physics of Ministry of Education, Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing 100871, China;
[2]Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China;
[3]Department of Physics, Chinese University of Hong Kong, New Territories, Hong Kong, China;
[4]National Synchrotron Radiation Research Center, Taiwan 30076, China;