1. Department of Materials Engineering, The University of Tokyo, 7-3-1 Hongo Bunkyo, Tokyo 113-8656, Japan
2. Department of Electrical and Electronic Information Engineering, Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku, Toyohashi, Aichi 441-8580, Japan
3. Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA