1. State Key Laboratory of Precision Measuring Technology and Instruments, School of Precision Instrument and Optoelectronics Engineering, Tianjin University, Tianjin 300072, China
2. Nanchang Institute for Microtechnology of Tianjin University, Tianjin 300072, China
3. Institut für Experimentalphysik, Johannes Kepler Universität Linz, Altenbergerstraße 69, A-4040 Linz, Austria
4. National Laboratory of Solid State Microstructures, School of Electronic Science and Engineering and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210008, China