1. Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, Nishi-ku, Fukuoka 819-0395, Japan.
2. Department of Advanced Materials Science and Engineering, Faculty of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan.
3. Research and Development Group, Hitachi, Ltd., Hatoyama, Saitama 350-0395, Japan.
4. Graduate School of Information Science and Technology, Osaka University, Suita, Osaka 565-0871, Japan.
5. The Ultramicroscopy Research Center, Kyushu University, Nishi-ku, Fukuoka 819-0395, Japan.
6. National Institute of Technology, Akashi College, Akashi, Hyogo 674-8501, Japan.