1. Department of Physics, Bar-Ilan University, 5290002 Ramat-Gan, Israel
2. Bar-Ilan Institute of Nanotechnology and Advanced Materials (BINA), 5290002 Ramat-Gan, Israel
3. Department of Chemistry and Center for NanoScience, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, 81377 München, Germany
4. Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, USA
5. Department of Chemical Engineering, Columbia University, New York, New York 10027, USA
6. Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, USA