1. Beijing
National Laboratory for Molecular Sciences, CAS Key Laboratory of
Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
2. University of Chinese Academy of Sciences, Beijing 100049, China
3. Department
of Physics and Astronomy, Shanghai Jiaotong University, Shanghai 200240, China
4. Materials
Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States