1. School of Space Science and Physics, Shandong University, Weihai 264209, China
2. Physical-Chemical Materials Analytical & Testing Center, Shandong University, Weihai 264209, China
3. School of Science, Langfang Normal University, Langfang 065000, China
4. School of Physics and Electronics, Shandong Normal University, Jinan 250014, China