1. CAS Key Laboratory of Nanosystem and Hierarchical Fabrication CAS Center for Excellence in Nanoscience National Center for Nanoscience and Technology Beijing 100190 P. R. China
2. Sino‐Danish Center for Education and Research Sino‐Danish College University of Chinese Academy of Sciences Beijing 100049 P. R. China
3. Niels Bohr Institute University of Copenhagen Copenhagen DK‐2100 Denmark
4. Department of Engineering Physics Tsinghua University Beijing 100084 P. R. China
5. National Engineering Laboratory for Dangerous Articles and Explosives Detection Technologies Beijing 100084 P. R. China
6. Key Laboratory of Particle and Radiation Imaging (Tsinghua University) Ministry of Education Beijing 100084 P. R. China
7. Center of Materials Science and Optoelectronics Engineering University of Chinese Academy of Sciences Beijing 100049 P. R. China