1. CAS Key Laboratory for Nanosystems and Hierarchical FabricationNanofabrication LaboratoryCAS Center for Excellence in NanoscienceNational Center for Nanoscience and Technology of China Beijing 100190 P. R. China
2. Center of Materials Science and Optoelectronics EngineeringUniversity of Chinese Academy of Sciences Beijing 100049 China
3. Department of ChemistrySchool of ScienceBeijing JiaoTong University Beijing 100044 P. R. China