1. Department of Electrical & Computer Engineering, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
2. Waterloo Institute for Nanotechnology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
3. University of Bordeaux, CNRS, Bx INP, ICMCB, UMR 5026, F-33600 Pessac, France