1. SMIT Center, School of Automation and Mechanical Engineering, Shanghai University, Shanghai, P. R., China
2. SMIT Center, School of Automation and Mechanical Engineering, Shanghai University, Shanghai, P. R. , China
3. SMIT Center, School of Automation and Mechanical Engineering, Shanghai University, Shanghai, P. R. China; Electronics Materials and Systems Laboratory, Department of Microtechnology and Nanoscience (MC2), Chalmers University of Technology, SE-412 96 Gothenburg, Sweden