1. Key Laboratory of Special Function Materials & Structure Design of the Ministry of Education, and School of Physical Science & TechnologyLanzhou University 222 South Tianshui Road Lanzhou 730000 China
2. Laboratory of Clean Energy Chemistry and Materials, State Key Laboratory of Solid Lubrication Lanzhou Institute of Chemical PhysicsChinese Academy of Sciences Lanzhou 730000 P. R. China
3. Center of Materials Science and Optoelectronics EngineeringUniversity of Chinese Academy of Sciences Beijing 100049 P. R. China