1. Department of Organic and Polymeric Materials, Graduate School of Science and Engineering, Tokyo Institute of Technology, O-okayama 2-12-1, Meguro-ku, Tokyo 152-8552, Japan
2. Department of Materials Structure Science, The Graduate University for Advanced Studies, Ibaraki 305-0801, Japan
3. Institute of Materials Structure Science, High Energy Accelerator Research Organization, Ibaraki 305-0801, Japan
4. Present address: Department of Applied Physics, Nagoya University Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
5. Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Kagamiyama 1-4-1, Higashi-Hiroshima 739-8527, Japan