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;
Institute of Chemistry;
Chinese Academy of Sciences;
Beijing 100190;
China;
Department of Physics;
Chinese University of Hong Kong;
New Territories;
Hong Kong;
China;
National Synchrotron Radiation Research Center;
Taiwan 30076;
China;