1. School of Electrical and Computer Engineering, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva, Southern Israel 8410501, Israel
2. Institut de Microelectrònica de Barcelona, Bellaterra, Catalonia 08193, Spain
3. Microfabrication and Exploratory Nanotechnology group, International Iberian Nanotechnology Laboratory, Braga, Norte 4715-330, Portugal
4. The Ilse-Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva 8410501, Israel