1. Shenzhen Key Laboratory of Hydrogen Energy and Department of Materials Science and Engineering Southern University of Science and Technology Shenzhen 518055 P. R. China
2. School of Physics and Technology Wuhan University Wuhan 430072 P. R. China
3. Physical Sciences and Engineering Division King Abdullah University of Science and Technology Thuwal 23955‐6900 Saudi Arabia
4. School of Electronic Science and Applied Physics Hefei University of Technology Hefei 230009 P. R. China