1. Advanced
Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
2. Department of Materials, ETH Zürich, Zürich CH-8093, Switzerland
3. Institute of Engineering Innovation, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-8656, Japan
4. Nanostructures Research
Laboratory, Japan Fine Ceramics Center, 2-4-1 Mutsuno,
Atsuta, Nagoya 456-8587, Japan
5. IBM Research Division, Zürich Research Laboratory, Rüschlikon CH-8803, Switzerland