1. Key
Laboratory of Novel Thin Film Solar Cells, Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, Hefei 230031, P. R. China
2. University of Science and Technology of China, Hefei 230000, P. R. China
3. Collaborative
Innovation Center of Radiation Medicine of Jiangsu Higher Education
Institutions, Soochow University, Suzhou 215123, P. R. China