1. State Key Laboratory of Precision Measuring Technology & Instruments, Centre of MicroNano Manufacturing Technology, Tianjin University, Tianjin 300072, China
2. Department of Physics and Helsinki Institute of Physics, University of Helsinki, P.O. Box 43,
FI-00014 Helsinki, Finland
3. Department of Electrical and Electronic Engineering, Southern University of Science and Technology,
Shenzhen 518055, China
4. Fraunhofer Institute for Integrated Systems and Device Technology IISB, Schottkystrasse 10, 91058
Erlangen, Germany