1. Department of Physics, Korea Advanced Institute of Science and Technology (KAIST) , Daejeon , South Korea
2. Korea Basic Science Institute (KBSI) , Seoul , South Korea
3. Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH) , Pohang , South Korea
4. National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory , Berkeley, CA , United States
5. Physics Department and Institute for Nanoscience and Engineering, University of Arkansas , Fayetteville, AR , United States
6. Graduate School of Semiconductor Technology, School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST) , Daejeon , South Korea