1. Pen-Tung Sah Institute of Micro-Nano Science & Technology, Xiamen University, Xiamen 361005, P. R. China
2. Fujian Micro/Nano Manufacturing Engineering Technology Research Center, Xiamen University, Xiamen 361102, P. R. China
3. Department of Mechanical & Electrical Engineering, Xiamen University, Xiamen 361005, P. R. China