1. Department of Electrical Engineering and BioscienceWaseda University 3‐4‐1 Ohkubo Shinjuku‐ku Tokyo 169‐8555 Japan
2. Research Institute for Materials Science and TechnologyWaseda University 3‐4‐1 Ohkubo Shinjuku‐ku Tokyo 169‐8555 Japan
3. Cooperative Major in Nuclear EnergyWaseda University 3‐4‐1 Ohkubo Shinjuku‐ku Tokyo 169‐8555 Japan