1. Department of Chemistry, Tsinghua University, Beijing 100084
2. Beijing Advanced Innovation Center for Imaging Technology and Key Laboratory of Terahertz Optoelectronics (MoE), Department of Physics, Capital Normal University, Beijing 100048
3. Applied Mechanics Laboratory, Department of Engineering Mechanics, School of Aerospace Engineering, Tsinghua University, Beijing 100084
4. Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB3 0FS
5. Materials Research Laboratory, University of California, Santa Barbara, Santa Barbara, CA 93106