1. Laboratory for Zero-Carbon Energy, Institute of Innovative Research, Tokyo Institute of Technology, 2−12−1 Ookayama, Meguro, Tokyo 152−8550, Japan
2. Department of Electrical and Electronic Engineering, Tokyo Institute of Technology, 2−12−1 Ookayama, Meguro, Tokyo 152−8550, Japan
3. Innovation Center, Mitsubishi Materials Corporation, 1002−14 Mukohyama, Naka, Ibaraki 311−0102, Japan
4. The Electron Microscopy Center, Tohoku University, 2−1−1 Katahira, Aoba, Sendai 980−8577, Japan
5. Institute of Applied Physics, University of Tsukuba, Tsukuba 305−8573, Japan