* Corresponding authors

^a School of Physics and Technology, University of Jinan, Shandong, P. R. China
E-mail: spsxuxj@ujn.edu.cn

^b Key Laboratory of Petroleum Resources, Gansu Province/Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Lanzhou 730000, P.R. China

^c Key Laboratory of Novel Thin Film Solar Cells, Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, 230031 Hefei, P. R. China
E-mail: lijx@ipp.ac.cn
Fax: +86-551-65591310
Tel: +86-551-65596617

^d NAAM Research Group, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia
E-mail: xkwang@ipp.ac.cn