1. College of Physics MIIT Key Laboratory of Aerospace Information Materials and Physics Key Laboratory for Intelligent Nano Materials and Devices Nanjing University of Aeronautics and Astronautics Nanjing 211106 P. R. China
2. School of Microelectronics Southern University of Science and Technology Shenzhen 518055 P. R. China
3. Department of Materials Science Fudan University Shanghai 200433 P. R. China