1. Nanomaterials Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8565, Japan
2. NGK Spark Plug-AIST Healthcare Materials Cooperative Research Laboratory, Anagahora, Shimo-Shidami, Moriyama-ku, Nagoya, Aichi 463-8560, Japan
3. NGK Spark Plug Co., Ltd., 2808 Iwasaki, Komaki, Aichi 485-8510, Japan