a
State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, P.R. China
E-mail: liangym@lzu.edu.cn
;
Fax: +86-931-8912582
;
Tel: +86-931-8912593
b
Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Science, Lanzhou 730000, P.R. China.