1. Department of Physics, University of Alberta, Edmonton, Alberta 26G 2R3, Canada
2. Department of Physics and Astronomy, University of Calgary, Calgary, Alberta T2N 1N4, Canada
3. Nanotechnology Research Centre (NANO), National Research Council Canada (NRC), Edmonton, Alberta T6G 2M9, Canada
4. Department of Physics, Florida Agricultural and Mechanical University, Tallahassee, Florida 32307, USA
5. Department of Chemistry, University of Alberta, Edmonton, Alberta 26G 2R3, Canada