1. Toray Research Center, Ohtsu, Shiga 520-8567, Japan
2. Department of Applied Physics, Waseda University, Okubo, Shinjuku-ku, Tokyo 169-8555, Japan
3. Department of Nanoscience and Nanoengineering, Waseda University, Okubo, Shinjuku-ku, Tokyo 169-8555, Japan
4. Department of Materials Science, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan