1. CAS Key Laboratory of Molecular Nanostructure and Nanotechnology Institute of Chemistry Chinese Academy of Sciences (CAS) Beijing 100190 P. R. China
2. School of Chemistry and Chemical Engineering University of Chinese Academy of Sciences Beijing 100049 P. R. China
3. Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences (CAS) Beijing 100190 P. R. China
4. Brookhaven National Laboratory Upton NY 11973 USA