1. Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University , 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
2. Graduate School of Information Science and Technology, Osaka University , 1-5 Yamadaoka, Suita, Osaka 565-0871, Japan
3. Research and Development Group, Hitachi, Ltd. , Akanuma 2520, Hatoyama, Saitama 350-0395, Japan
4. The Ultramicroscopy Research Center, Kyushu University , 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan