1. Department of Nuclear Science and Engineering and Department of Materials Science and Engineering Massachusetts Institute of Technology Cambridge MA 02139 USA
2. Advanced Materials Processing and Analysis Center University of Central Florida Orlando FL 32816 USA
3. IBS Center for Integrated Nanostructure Physics Institute for Basic Science (IBS) Sungkyunkwan University Suwon 440‐746 Republic of Korea
4. School of Materials Science and Engineering Shanghai Jiao Tong University Shanghai 200240 China
5. Department of Materials Science and Engineering Pohang University of Science and Technology Pohang 790‐784 Republic of Korea
6. Division of Electron Microscopic Research Korea Basic Science Institute 113 Gwahangno Yuseong‐Gu Daejeon 305‐333 Republic of Korea