[1] School of Physics and Material Science, Anhui University, Hefei 230039, China
[2] Key Laboratory for Thin Film and Microfabrication Technology of Ministry of Education, Research Institute of Micro/Nano Science and Technology, Shanghai Jiaotong University, Shanghai 200240, China
[3] Research Organization of Science and Technology, Ritsumeikan University, Kusatsu 525-8577, Japan