1. Department of Advanced Materials Engineering, Daejeon University, Daejeon 34520, Republic of Korea
2. Vacuum Materials Measurement Team, Korea Research Institute of Standards and Science, Daejeon 34113, Republic of Korea
3. Department of Electrical Engineering, Hanyang University, Seoul 04763, Republic of Korea
4. Division of Nanoscience and Technology, University of Science and Technology, Daejeon 34113, Republic of Korea