1. Department of Materials Science and Engineering, Tokyo Institute of Technology, Meguro, Tokyo 152-8552, Japan
2. Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Meguro, Tokyo 152-8552, Japan
3. Condensed Matter Research Center and Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan