1. State Key Laboratory of Physical Chemistry of Solid Surfaces College of Materials Xiamen University Xiamen Fujian 361005 China
2. Institute of Physics Chinese Academy of Sciences Beijing 100190 China
3. Center for Memory and Recording Research Building UC San Diego La Jolla CA 92093 USA
4. Department of Energy Politecnico di Milano Via Lambruschini, 4 Milano 20156 Italy
5. College of Chemistry and Materials Engineering Wenzhou University Wenzhou 325035 China
6. Center of Electron Microscopy and State Key Laboratory of Silicon Materials School of Materials Science and Engineering Zhejiang University Hangzhou 310027 China
7. Shenzhen Research Institute of Xiamen University Shenzhen 518000 China