1. School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245, United States
2. Hunan Key Laboratory for Super-microstructure and Ultrafast Process, School of Physics and Electronics, Central South University, Changsha, Hunan 410083, People’s Republic of China
3. School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou 221116, People’s Republic of China
4. Solid-State Electronics, The Ångström Laboratory, Uppsala University, SE-751 21, Uppsala, Sweden
5. Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 100083, People’s Republic of China