1. Electrical and Computer Engineering Department and Russell Berrie Nanotechnology Institute, Technion , Haifa , 32000 , Israel
2. Technische Physik , Institute of Nanostructure Technologies and Analytics, Center of Interdisciplinary Nanostructure Science and Technology (CINSaT), University of Kassel , Heinrich-Plett-Str. 40, 34132 Kassel , Germany