1. Contribution from the Advanced Nano Materials Laboratory (ANML) and High Voltage Electron Microscopy Station (HVEMS), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan, Quantum Beam Science Directorate, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan, Institute for Chemical Research, Kyoto University, Uji, Kyoto-fu 611-0011, Japan, and PRESTO, Japan Science and Technology Corporation (JST), Kawaguchi, Saitama 332-0012, Japan