1. Key
Lab of Microsystem and Microstructure of the Ministry of Education, Harbin Institute of Technology, No. 2 YiKuang Street, Harbin 150080, P. R. China
2. Materials
Physics and Chemistry, Harbin Institute of Technology, No. 92
Xidazhi Street, Harbin 150080, P. R. China
3. Department
of Mathematics and Materials Research Institute, Pennsylvania State University, University Park, Pennsylvania 16802, United States
4. State
Key Laboratory of Robotics and Systems, Harbin Institute of Technology, Harbin, P. R. China