1. Center for Electronic Materials, Korea Institute of Science and Technology, Seoul 02792, Republic of Korea
2. Division of Quantum Phases and Devices, Department of Physics, Konkuk University, Seoul 05029, Republic of Korea
3. Advanced Analysis Center, Korea Institute of Science and Technology, Daejeon 34113, Republic of Korea
4. Division of Nano and Information Technology, KIST-School, University of Science and Technology, Seoul 02792, Republic of Korea