1. a Department of Physics , National Cheng Kung University , Tainan , 70101 , Taiwan , ROC
2. b Center for Micro/Nano Science of Technology , National Cheng Kung University , Tainan , 70101 , Taiwan
3. c Institute of Physics , St. Petersburg State University , St. Petersburg , Petrodvorets , 198504 , Russia
4. d Blagoveschensk State Pedagogical University , Blagoveschensk , 675002 , Russia
5. e Faculty of Physics and Geosciences , University of Leipzig , Leipzig , D-04103 , Germany