1. International Center for Materials Nanoarchitectonics (MANA) and Center for Functional Sensor & Actuator (CFSN), National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan.
2. Center for Exploratory Research, Research & Development Group, Hitachi Ltd., Akanuma 2520, Hatoyama-machi, Hiki-gun, Saitama 350-0395, Japan.