1. Department of Materials Science and Engineering, Kyoto University, Kyoto 606-8501, Japan
2. Departamento de Física de Materiales, Universidad Complutense de Madrid, Madrid 28040, Spain
3. Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
4. Nanoelectronics Research Institute, National Institute of Advanced Industrial Science and Technology, Ibaraki 305-8568, Japan
5. Department of Applied Chemistry, Hiroshima University, Hiroshima 739-8527, Japan