[1] JEOL Datum Inc, Japan
[2] JEOL Co. Ltd, 3-1-2 Musashino, Akishima, Tokyo,196, Japan
[3] Materials Research Center, TDK Co, 570-2 Matsugashita, Minami-hatori, Narita,286, Japan
[4] Department of Electronics and Information Science, Kyoto Institute of Technology, Matsugasaki, Kyoto,606, Japan