1. Russell Berrie Nanotechnology Institute, Technion, 32000 Haifa, Israel
2. Andrew and Erna Viterbi Faculty of Electrical Engineering, Technion, 32000 Haifa, Israel
3. E. L. Ginzton Laboratory, Department of Applied Physics, Stanford University, Stanford, California 94305, USA
4. Institute of Nanostructure Technologies and Analytics, Technische Physik, CINSaT, University of Kassel, 34132 Kassel, Germany