a
School of Chemistry and Chemical Engineering, Shandong University, P. R. China
E-mail: wjiang@sdu.edu.cn
;
Fax: +86 531 8856446
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Tel: +86 531 88363888
b
National Center for Nanoscience and Technology, 11 Bei Yi Tiao, ZhongGuanCun, P. R. China
E-mail: dingbq@nanoctr.cn
;
Fax: +86 10 62656765
;
Tel: +86 10 82545636
c
Institute of Modern Physics, Chinese Academy of Sciences, P. R. China