1. Department of Chemistry and the Waterloo Institute for Nanotechnology, University of Waterloo, Waterloo, ON N2L 3G1, Canada
2. Department of Materials Science and Engineering, University of California, Berkeley, California 94720, United States
3. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
4. Faculty of Engineering, Hokkaido University, Sapporo 060-8628, Japan