1. Racah Institute of Physics and the Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
2. Applied Physics Department the Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
3. Department of Physics, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
4. Chemical Service Unit, Weizmann Institute of Science, Rehovot 76100, Israel