1. Nanotechnology Research Centre, National Research Council of Canada, Edmonton, Alberta T6G 2M9, Canada
2. Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E1, Canada
3. Quantum Silicon Inc., Edmonton, Alberta T6G 2M9, Canada
4. Department of Electrical and Computer Engineering, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
5. School of Engineering, Stanford University, Stanford, California 94305, United States
6. Canadian Bank Note Company, Ottawa, Ontario K1Z 1A1, Canada