1. Department of Electrical Engineering, Technion, Haifa 32000, Israel
2. Russell Berrie Nanotechnology Institute, Technion, Haifa 32000, Israel
3. Material Science and Engineering Department, Technion, Haifa 32000, Israel
4. Applied Physics Department, Rachel and Selim Benin School of Computer Science and Engineering, The Hebrew University of Jerusalem, Jerusalem 9190401, Israel