1. Department of Physics, The Chinese University of Hong Kong, Shatin 852, Hong Kong SAR, China
2. Shaanxi Key Laboratory for Advanced Energy Devices, Shaanxi Engineering Lab for Advanced Energy Technology, School of Materials Science and Engineering, Shaanxi Normal University, Xi’an 710119, China
3. Department of Chemistry, The Chinese University of Hong Kong, Shatin 852, Hong Kong SAR, China