1. Materials
and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori, Yokohama 226-8503, Japan
2. Department
of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan
3. Quantum
Beam Science Center, Japan Atomic Energy Agency, Sayo, Hyogo 679-5148, Japan