1. Department of Physics, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, China
2. School of Energy and Environment, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, China
3. X-Ray Science Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
4. Center for Green Research on Energy and Environmental Materials (GREEN), National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
5. Shenzhen Research Institute, City University of Hong Kong, Shenzhen 518057, China