1. Beijing Key Laboratory of Microstructure and Properties of SolidsInstitute of Microstructure and Properties of Advanced MaterialsBeijing University of Technology Beijing 100124 China
2. College of Materials Science and EngineeringHunan University Changsha 410082 China
3. Beijing Key Laboratory of Green Chemical Reaction Engineering and TechnologyDepartment of Chemical EngineeringTsinghua University Beijing 100084 P. R. China
4. School of Physics and ElectronicsHunan University Changsha 410082 China
5. Department of Nuclear Engineering and Radiological SciencesUniversity of Michigan Ann Arbor MI 48109 USA