1. International Center for Young Scientists (ICYS), High Voltage Electron Microscopy Station (HVEMS), and Advanced Materials Laboratory (AML), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan, Research Reactor Institute, Kyoto University, Kumatori-cho, Osaka 590-0494, Japan, and Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan