1. State Key Laboratory of Functional Materials for Informatics Shanghai Institute of Microsystem and Information Technology Chinese Academy of Sciences Shanghai 200050 China
2. University of Chinese Academy of Sciences Beijing 10049 China
3. Institute of Ion Beam Physics and Materials Research Helmholtz‐Zentrum Dresden‐Rossendorf Bautzner Landstrasse 400 Dresden 01328 Germany
4. Department of Physics Shanghai University 99 Shangda Road Shanghai 200444 China
5. Institute of Radiation Physics Helmholtz‐Zentrum Dresden‐Rossendorf Bautzner Landstrasse 400 Dresden 01328 Germany
6. College of Science Nanjing University of Aeronautics and Astronautics Nanjing 211106 China
7. Department of Physics and Astronomy Stony Brook University Stony Brook NY 11794 USA