1. Micro and Nano System Research Center, College of Information and Computer, Taiyuan University of Technology, Taiyuan 030024, P. R. China
2. Guangdong Provincial Key Laboratory of Electronic Functional Materials and Devices, Huizhou University, Huizhou 516001, P. R. China
3. Department of Advanced Materials Science and Engineering, Faculty of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan