1. Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba 277-8561
2. Institute for Materials Research, Tohoku University, Sendai 980-8577
3. CREST, Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012
4. Xintek Inc., 308 West Rosemary Street, Chapel Hill, NC 27516, U.S.A.
5. Department of Physics and Astronomy and Curriculum in Applied and Materials Sciences, University of North Carolina, Chapel Hill, NC 27599, U.S.A.
6. Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531